Title: Display substrate and display device
Abstract: A display substrate comprising a plate, for example a glass plate, on which display elements, e.g. pixels comprising pixel electrodes and thin-film-transistors, and an acoustic transducer, e.g. a microphone, speaker or buzzer, formed from thin film layers over a cavity, are formed. The cavity may be provided by powderblasting through the depth of the glass plate. The display substrate with integrated acoustic transducer may be incorporated in a display device, e.g. a liquid crystal display device. Also described is a discrete acoustic transducer, comprising a plate of an insulating material, a cavity in the plate, a plurality of layers that have been deposited on the plate, and a moveable member formed from the deposited layers and positioned over the cavity.
Patent Number: 6,940,564 Issued on 09/06/2005 to Murden, et al.
| Inventors:
|
Murden; Vega (London, GB);
Green; Peter W. (Reigate, GB)
|
| Assignee:
|
Koninklijke Philips Electronics N.V. (Eindhoven, NL)
|
| Appl. No.:
|
099758 |
| Filed:
|
March 15, 2002 |
Foreign Application Priority Data
| Current U.S. Class: |
349/1; 381/190 |
| Intern'l Class: |
G02F 001/13 |
| Field of Search: |
349/1
367/178,179,180,181
381/190
257/59
|
References Cited [Referenced By]
U.S. Patent Documents
| 5130829 | Jul., 1992 | Shannon.
| |
| 5146435 | Sep., 1992 | Bernstein.
| |
| 5303210 | Apr., 1994 | Bernstein.
| |
| 5335210 | Aug., 1994 | Bernstein.
| |
| 5452268 | Sep., 1995 | Bernstein.
| |
| 5940015 | Aug., 1999 | Thornton et al.
| |
| 5956292 | Sep., 1999 | Bernstein.
| |
| 6427017 | Jul., 2002 | Toki.
| |
| Foreign Patent Documents |
| 0979992 | Feb., 2000 | EP.
| |
| 2343811 | May., 2000 | GB.
| |
| WO0009440 | Feb., 2000 | WO.
| |
| WO0012428 | Mar., 2000 | WO.
| |
Other References
"Piezoelectric Cantilever Microphone and Microspeaker", Seung S. Lee et al.,
Journal of Microelectromechanical Systems, vol. 5, No. 4, Dec. 1996.
"Design and Fabrication of Silicon Condenser Microphone Using Corrugated Diaphragm
Technique", Quanbo Zou et al., Journal of Microelectromechanical System, vol. 5,
No. 3, Sep. 1996.
|
Primary Examiner: Chowdhury; Tarifur R.
Assistant Examiner: Chung; David Y.
Claims
1. A display substrate, comprising:
a plate;
at least one display element formed on the plate; and
an acoustic transducer formed on the plate over a cavity;
wherein the cavity is formed in the plate.
2. A display substrate according to claim 1, wherein
the acoustic transducer is a microphone or a speaker, and comprises a fixed electrode
and a diaphragm comprising a vibrating electrode.
3. A display substrate, comprising:
a plate;
at least one display element formed on the plate; and
an acoustic transducer formed on the plate over a cavity;
wherein
the acoustic transducer is a microphone or a speaker, and comprises a fixed electrode
and a diaphragm comprising a vibrating electrode, and
the vibrating electrode is formed from a same layer of conductor as at least a
first part of the one or more display elements.
4. A display substrate, comprising:
a plate;
at least one display element formed on the plate; and
an acoustic transducer formed on the plate over a cavity;
wherein
the acoustic transducer is a microphone or a speaker, and comprises a fixed electrode
and a diaphragm comprising a vibrating electrode, and
the fixed electrode is formed from a same layer of conductor as at least a second
part of the one or more display elements.
5. A display substrate according to claim 2, wherein
the diaphragm further comprises an insulation layer.
6. A display substrate according to claim 5, wherein
the insulation layer of the diaphragm is formed from a same insulation layer
as at least a part of the at least one display component.
7. A display substrate according to claim 3, wherein
the cavity is between the acoustic transducer and a surface of the plate.
8. A display substrate according to claim 3,
wherein the cavity is formed in the plate.
9. A display substrate according to claim 1, wherein
the cavity extends the whole depth of the plate.
10. A display substrate according to claim 1, wherein
the cavity is a powderblasted cavity.
11. A display substrate, comprising;
a plate;
at least one display element formed on the plate; and
an acoustic transducer formed on the plate over a cavity;
wherein
the at least one display element forms an active matrix array such that the display
substrate is an active matrix substrate for a liquid crystal display device.
12. A display substrate according to claim 11 wherein
the active matrix array comprises thin-film-transistors and
the vibrating electrode is formed from a same layer of conductor as the gates
of the thin-film-transistors.
13. A display substrate according to claim 11, wherein
the active matrix array comprises pixel electrodes and
the fixed electrode is formed from a same layer of conductor as the pixel electrodes.
14. A display substrate according to claim 8, wherein
the at least one display element is a common electrode such that the display
substrate is a passive substrate for a liquid crystal display device.
15. A display substrate according to claim 3, wherein
the at least one display element forms an active matrix array such that the display
substrate is an active matrix substrate for a liquid crystal display device.
16. A display substrate according to claim 15, wherein
the active matrix array comprises thin-film-transistors and
the vibrating electrode is formed from a same layer of conductor as the gates
of the thin-film-transistors.
17. A display substrate according claim 4, wherein
the at least one display element forms an active matrix array such that the display
substrate is an active matrix substrate for a liquid crystal display device.
18. A display substrate according to claim 17, wherein
the active matrix array comprises thin-film-transistors and
the vibrating electrode is formed from a same layer of conductor as the gates
of the thin-film-transistors.
19. A display substrate according to claim 17, wherein
the active matrix array comprises pixel electrodes and
the fixed electrode is formed from a same layer of conductor as the pixel electrodes.
20. A display substrate according to claim 4, wherein
the cavity is between the acoustic transducer and a surface of the plate.
21. A display substrate according to claim 4, wherein
the cavity is formed in the plate.
22. A display substrate according to claim 11, wherein
the acoustic transducer is a microphone or a speaker, and comprises a fixed electrode
and a diaphragm comprising a vibrating electrode.
23. A display substrate according to claim 11, wherein
the cavity is between the acoustic transducer and a surface of the plate.
24. A display substrate according to claim 11, wherein
the cavity is formed in the plate.
Description
The present invention relates to display substrates, and display devices, for
example liquid crystal display devices, incorporating display substrates. The present
invention also relates to acoustic transducers.
Many electrical products, for example portable computers, personal organisers,
and mobile telephones, include one or more display devices and one or more acoustic transducers.
Known display devices include liquid crystal, plasma, polymer light emitting
diode, organic light emitting diode and field emission display devices. Such devices
typically comprise two opposing display substrates with an electrically controllable
light modulation layer or array between the two display substrates. The light modulation
layer or array is provided either on one of the display substrates or in a gap
between the two display substrates. A typical liquid crystal display device, with
one of the display substrates having an active matrix of thin film transistors
(TFTs) is disclosed in U.S. Pat. No. 5,130,829.
Examples of commonly used acoustic transducers are microphones, speakers
and piezoelectric buzzers. Often electrical products require two or more acoustic
transducers. For example, mobile telephones typically require a microphone for
voice input, a speaker for audio output, e.g. speech, and a buzzer to attract a
user's attention.
There is a trend for electrical products to provide increasing levels of functionality,
and consequently more information is required to be displayed to users of the products.
Hence larger area display devices are required. Conversely, however, there is a
trend for products to be made smaller, especially in the case of portable equipment.
For example, ever smaller mobile telephones require ever larger displays for purposes
of displaying text messages and Internet content.
Consequently the space available for components such as acoustic transducers,
in products also including display devices, is becoming increasingly scarce. A
known solution for alleviating this problem is to provide and use smaller acoustic
transducers. However, generally, as components are reduced in size, their unit
production costs increase. Also, their assembly, connection and testing in an end
product becomes more burdensome.
Considering, in isolation, the provision of small acoustic transducers,
it is known within the field of acoustic transducers (quite separately from consideration
of their use with display devices) to form acoustic transducer units using thin
film layers deposited on silicon wafers. Such acoustic transducers are disclosed
in "Design and Fabrication of Silicon Condenser Microphone Using Corrugated Diaphragm
Technique", Quanbo Zou et al., Journal of Microelectromechanical Systems, Vol.
5, No. 3, September 1996; "Piezoelectric Cantilever Microphone and Microspeaker",
Seung S. Lee et al., Journal of Microelectromechanical Systems, Vol. 5, No. 4,
December 1996; and EP-A-0 979 992. Multiple acoustic transducers can be formed
on each silicon wafer in conventional batch processing manner, and individual acoustic
transducers thereafter formed by slicing of the wafer. The production techniques
involved are often termed "micromachining".
These types of acoustic transducers can be produced in miniature form. The
thin film layers can also be used to form integral semiconductor circuitry required
for operation of the acoustic transducers. However, in products where space is
at a premium due to the inclusion of one or more display devices, the use of such
acoustic transducers would not fully resolve the problem of lack of space, because
the packaging of each acoustic transducer would need its own space in the end product.
Moreover, insertion and connection of the acoustic transducer in the end product
would be particularly burdensome due to the very miniaturisation advantage that
such acoustic transducers might provide.
Overall, therefore, it is desirable to provide an alternative solution,
other than simple reduction in size of acoustic transducers, to the problems described above.
In a first aspect, the present invention provides a display substrate, comprising:
a plate; one or more display components formed on the plate; and an acoustic transducer
formed on the plate over a cavity.
In a second aspect, the present invention provides a display device comprising
a display substrate according to the first aspect.
The present invention derives from the idea of providing an integrated display
and acoustic transducer by forming the acoustic transducer as an integrated part
of one of the display substrates of a display device. Thus space can be saved in
a product requiring both a display device and an acoustic transducer. Moreover,
the requirement to separately insert and connect the acoustic transducer into an
end product is removed as these operations occur when the display device is inserted
and connected. This is particularly advantageous when the acoustic transducer is
formed in miniature form on the substrate of the display device.
Preferably, the plate from which the display substrate is formed is of
glass, quartz or a plastics material. This allows particularly economical display
devices to be produced as such materials are commonly used as substrate materials
for conventional display devices.
In a third aspect, the present invention provides a method of forming a display
substrate, comprising: providing a plate; forming one or more display components
on the plate; and forming an acoustic transducer on the plate over a cavity.
In a fourth aspect, the present invention provides a method of forming a display
device, comprising forming a display substrate using a method according to the
third aspect.
The cavity may be formed in the plate, in which case the cavity may extend through
the whole depth of the substrate. Preferably, the cavity is produced by powderblasting,
as this allows the provision of cavities in strong plate materials.
The cavity may alternatively be formed between the acoustic transducer and a
surface of the plate, by the use of one or more sacrificial layers. This allows
flexibility of design.
The joint provision of an acoustic transducer as well as one or more display
elements on the same substrate allows process steps, in particular deposition and/or
etching of various thin film layers, to be shared, thus simplifying the production
process. The acoustic transducer may be a microphone or speaker, comprising a fixed
electrode and a moveable diaphragm comprising a diaphragm electrode. In this case,
the diaphragm electrode is preferably formed from a same layer of conductor as
at least a first part of respective display elements formed on the display substrate.
Further, the fixed electrode is preferably formed from a same layer of conductor
as at least a second part of respective display elements formed on the display
substrate. The moveable diaphragm may further comprise an insulation layer, in
which case this insulation layer is preferably formed from a same insulation layer
as at least a part of respective display elements, thus simplifying the production
process. However, the insulation layer (or indeed any other layer) may be provided
separately for the purpose of optimising the performance characteristics of the
acoustic transducer and the display element individually.
Preferably the display substrate is an active matrix display substrate
for a liquid crystal display device, and the display elements include thin-film
transistors and pixel electrodes. In this case, the diaphragm electrode is preferably
formed from a same layer of conductor as the gates of the thin-filmtransistors,
and the fixed electrode is preferably formed from a same layer of conductor as
the pixel electrodes.
When the display device is intended for an end product that requires more than
one acoustic transducer, a plurality of acoustic transducers may be provided on
one display substrate, thus multiplying the benefits derived from the present invention.
In a fifth aspect, the present invention provides an acoustic transducer, comprising:
a substrate of an insulating material; a cavity in the substrate; a plurality of
layers which have been deposited on the substrate; and a moveable member formed
from the deposited layers and positioned over the cavity.
In a sixth aspect, the present invention provides a method of forming an acoustic
transducer, comprising: providing a substrate of an insulating material; depositing
a plurality of layers on the substrate; forming a cavity in the substrate; and
forming, from the deposited layers, a moveable member positioned over the cavity.
Preferably, a fixed electrode is formed opposing the moveable member;
the moveable member is formed from a moveable electrode formed from a first metal
layer, the first metal layer being one of the plurality of layers, and an insulating
layer, the insulating layer being another one of the plurality of layers; and the
fixed electrode is formed from a second metal layer, the second metal layer being
another one of the plurality of layers.
Preferably, the cavity is formed by powderblasting.
The fifth and sixth aspects are derived from the realisation that acoustic transducers
derived as part of the above mentioned first to fourth aspects of the present invention
also provide potential benefits over known acoustic transducers even when not integrated
as such on a display substrate. For example, by forming such acoustic transducers
by depositing layers on an insulating substrate and forming a cavity in the insulating
substrate, effective miniature acoustic transducers can be made from strong cheap
substrate materials, thus reducing packaging and/or processing and/or material
costs compared to the known silicon wafer based acoustic transducers discussed
earlier above. Alternatively, or additionally, acoustic transducers according to
the fifth and sixth aspects may, by virtue of their features common with display
substrates, be provided such that their external physical form or packaging makes
their incorporation into end products alongside display devices more straightforward
than that of conventional acoustic transducers.
The dependent claims define, in addition to the various preferences discussed
above, yet further preferences or possibilities of the present invention.
The above described and other aspects of the invention will be apparent from
and elucidated with reference to the embodiments described hereinafter.
Embodiments of the present invention will now be described, by way of
example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic illustration of part of a display substrate with an integrated microphone;
FIG. 2 is a schematic illustration of a cross-section of a liquid crystal display
device comprising the display substrate illustrated in FIG. 1;
FIG. 3 is a flowchart showing process steps employed for producing the display
substrate shown in FIGS. 1 and 2;
FIGS. 4
a-f schematically illustrate the build-up of the features of
the display substrate 1 as the process of FIG. 3 progresses;
FIG. 5 is a flowchart showing the process steps employed for producing a condenser microphone;
FIGS. 6
a and 6
b schematically illustrate the build-up
of the features of the condenser microphone as the process of FIG. 5 progresses;
FIG. 7
a is a schematic illustration of a piezoelectric buzzer comprising
a diaphragm over a cavity;
FIG. 7
b is a schematic illustration of a piezoelectric buzzer comprising
a cantilever over a cavity;
FIG. 7
c is a schematic illustration of another piezoelectric buzzer comprising
a diaphragm over a cavity; and
FIG. 7
d is a schematic illustration of another piezoelectric buzzer comprising
a cantilever over a cavity.
It should be noted that the figures are diagrammatic and not drawn to scale.
Relative
dimensions and proportions of parts of these figures have been shown exaggerated
or reduced in size, for the sake of clarity and convenience in the drawings.
FIG. 1 is a schematic illustration of part of a display substrate
1 provided
in a first embodiment. The display substrate
1 comprises a glass plate
2.
As with conventional display substrates, plural display elements are provided on
the upper surface (as viewed in FIG. 1) of the glass plate
2. The term "display
element" is used herein to refer to any item included as a part of a display substrate
that contributes to the display functionality of the display substrate. In this
embodiment, the plural display elements include an array of pixels. A large number
of such pixels are provided, but for clarity only five of these, namely pixels
4,
5,
6,
7 and
8, are shown in FIG.
1.
A microphone
10, i.e. one type of acoustic transducer, is also provided
on the upper surface of the glass plate
2. In this embodiment the shape
of the microphone as viewed from above the upper surface of the glass plate
2
is approximately circular. The microphone
10 is a condenser microphone comprising
a fixed electrode and a vibrating electrode. An external contact is provided for
each of these microphone electrodes, i.e. contact
12 for the vibrating electrode
and contact
13 for the fixed electrode. In operation of the microphone
10,
the capacitance between the two electrodes varies as the vibrating electrode moves
relative to the fixed electrode in response to sound waves. By connecting a suitable
circuit to the two external contacts, this varying capacitance may be measured
and processed.
The pixels
4,
5,
6,
7,
8 include TFTs and
form an active matrix array such that the display substrate
1 may be used
as an active matrix display substrate of a liquid crystal display device
11,
as schematically illustrated in FIG. 2 where the display substrate
1 is
shown in cross-section through the line X
1-X
2 of FIG.
1.
In FIG. 2, the glass plate
2, the microphone
10 and the contact
12
are individually indicated. However, for clarity, the pixels
4,
5,
6 and any other display elements along the line X
1-X
2 are
represented together as an active matrix layer
14 formed on the surface
of the glass plate
2.
The glass plate
2 has a cavity
28 extending through the whole depth
of the glass plate
2. The microphone
10 is formed over the cavity
28. The cavity
28 is of approximately circular cross-section, and
this provides the approximately circular shape of the microphone
10, as
will be explained in more detail below.
The contact
12 for the vibrating electrode is provided on the glass plate
2 next to the microphone
10 at a position outside of the area covered
by the active matrix layer
14.
The area of the glass plate
2 that is covered by the active matrix layer
14 is used to form a liquid crystal display area as follows. The glass plate
2 has a liquid crystal orientation layer
20 deposited over the active
matrix layer
14. The liquid crystal display device
11 further comprises
a second glass plate
16, with a common electrode
18 thereon, spaced
apart from the glass plate
2. The second glass plate
16 has a liquid
crystal orientation layer
22 deposited over the common electrode
18.
A liquid crystal layer
24, comprising twisted nematic liquid crystal material,
is disposed between the orientation layers
20,
22 of the two glass
plates
2,
16. A seal
26 is provided between the two orientation
layers
20,
24 at the edge of the area of coverage of the liquid crystal
layer
24. These and other details of the liquid crystal display device (in
so far as the area corresponding to the active matrix layer
14, in contrast
to the microphone
10, is concerned) are the same, and operate the same,
as the liquid crystal display device disclosed in U.S. Pat. No. 5,130,829, the
contents of which are contained herein by reference.
Alternatively, the liquid crystal layer may extend over the microphone
in order to simplify the production process, in which case the microphone will
still respond to sound by virtue of vibrations passing through the liquid crystal
layer, although this will usually have a detrimental affect on the quality of the
microphone response.
FIG. 3 shows the process steps employed in this embodiment for producing the
display substrate
1. These process steps will now be described, with the
aid of FIGS. 4
a-f which schematically illustrate the build-up of the features
of the display substrate
1 as the process progresses. In FIGS. 4
a-f,
the display substrate
1 is shown in terms of the cross-section through the
line X
1-X
3of FIG. 1, i.e. to include the contact
12
for the vibrating electrode, the microphone
10, and just the single pixel
4. It will be appreciated however, that the procedures described below in
relation to the pixel
4 are in fact performed at the same time for the whole
array of pixels.
The features shown in FIG. 4
a are formed as follows. At step s
2,
the glass plate
2 is provided. At step s
4, an initial powderblast
resist layer
42 is deposited on the surface of the glass plate
2
over the area where the microphone
10 is to be provided. At step s
6,
a metal layer is deposited, and patterned to form a gate
44 where the TFT
of the pixel
4 is to be formed. At step s
8, a first silicon nitride
(SiN) layer
48, i.e. an insulation layer, is deposited over substantially
the whole area of the glass plate
2. At steps slO and s
12, two amorphous
silicon layers, for the TFT being formed, are deposited. More particularly, at
step slO an undoped amorphous silicon layer
50 is deposited over the first
SiN layer
48 above the gate
44, followed at step s
12 by an
n+amorphous silicon layer
52, thus forming the overall structure shown in
FIG. 4
a.
The additional features shown in FIG. 4
b are formed as follows. At step
s
14, a further metal layer is deposited and patterned to provide a source
56 and a drain
58 for the TFT being formed, and an electrode which
will serve as the microphone vibrating electrode
60 of the microphone being
formed. The n+amorphous silicon layer
52 is also removed in a small area
over the gate
44. Thus the overall structure shown in FIG. 4
b is
arrived at.
The additional features shown in FIG. 4
c are formed as follows. At step
s
16, a second SiN layer
62, i.e. insulation layer, is deposited over
substantially the whole area of the glass plate
2. By virtue of this, fabrication
of the TFT
69 is essentially completed. At step sl
8, through holes
are etched in the second SiN layer
62, in particular a hole
66 over
the drain
58, and a hole
68 over an extended portion of the microphone
vibrating electrode
60. Thus the overall structure shown in FIG. 4
c is
arrived at.
The additional features shown in FIG. 4
d are formed as follows. At step
s
20, a transparent electrode layer of indium tin oxide (ITO) is deposited
over the second SiN layer
62 and the holes
64,
66 and
68
therein, and patterned to form a pixel electrode
72, a drain terminal
74
connecting the drain
58 of the TFT
69 to the pixel electrode
72,
an electrode which will serve as the microphone fixed electrode
76, the
microphone fixed electrode contact
13 mentioned earlier with reference to
FIG. 1 (but not shown here in FIG. 4
d as it does not fall on the cross-section
line X
1-X
3), and the contact
12 (mentioned earlier
with reference to FIGS. 1 and 2) for the microphone vibrating electrode
60.
In order that the microphone fixed electrode
76 will remain substantially
stationary in operation whilst the earlier described microphone vibrating electrode
60 will vibrate, the ITO layer is made thicker than the joint thickness
of the first SIN layer
48 and the microphone vibrating electrode
60,
by an amount dependent on the relative stiffness of the materials involved. The
microphone fixed electrode
76 is patterned such as to include gaps
80,
81,
82, and
83 therein, such that when the microphone fixed
electrode
76 is viewed from above it is in the form of a mesh. (When the
microphone is completed, these gaps will form acoustic air holes, as will be described
in more detail below.) Thus the overall structure shown in FIG. 4
d is arrived at.
The additional features shown in FIG. 4
e are formed as follows. At step
s
22, a second powderblast resist layer
43 is deposited over the whole
area of the bottom surface of the glass plate
2 except for the area corresponding
to where the microphone
10 is to be provided. In this embodiment the cavity
is of diameter ˜1 mm-2 mm, although generally this may be varied according
to the required acoustic response of the microphone. At step s
24, powderblasting,
using iron pellets, is performed on the bottom surface of the glass plate
2,
to form a cavity
28 through the whole depth of the glass plate
2.
During the powderblasting process, the remaining area of the bottom surface of
the glass plate
2 is protected by the second powderblast resist layer
43.
As the cavity nears completion, i.e. as the powderblasting works its way toward
the underneath of the first SiN layer
48 in the area of the cavity, the
first SiN layer
48 is protected by the first powderblast resist layer
42.
During the powderblasting process the top surface of the overall structure may
optionally be protected by a layer, for example an organic photoresist, applied
thereto before the powderblasting and removed by etching thereafter. In addition,
the front side of the plate may be protected by, for example, a plate (e.g. metal)
which is used to mount the glass plate during the powderblasting. Further details
of the powderblasting process and powderblasting resists are given below. Thus
the overall structure shown in FIG. 4
e is arrived at.
The additional features shown in FIG. 4
f are formed as follows. At step
s
26, the powderblast resist layers
42 and
43 are removed by
etching. At step s
28, the second SiN layer
62 is removed by etching
in the area where the microphone
10 is to be provided. This leaves an acoustic
cavity
92 between the microphone fixed electrode
76 and the microphone
vibrating electrode
60, and consequently the earlier mentioned gaps
80,
81,
82 and
83 form acoustic air holes connected to the acoustic
cavity
92. A further effect of the removal of the second SiN layer
62
in this area is to leave the first SiN layer
48 in the area over the cavity
28 and the microphone vibrating electrode
60 suspended over the cavity.
In this way the microphone vibrating electrode
60, and the portion of the
first SiN layer
48 attached thereto, together form a vibrating diaphragm
94 of the microphone
10. Furthermore, the removal of the second SiN
layer
62 at step s
28 completes the formation of the microphone
10,
which comprises the microphone fixed electrode
76 and the vibrating diaphragm
94, along with the acoustic cavity
92 and acoustic air holes
80,
81,
82 and
83 defined thereby.
In addition to the microphone
10, other completed functional items indicated
in FIG. 4
f are the pixel
4 and the microphone vibrating electrode
contact
12.
The pixel
4 comprises the pixel electrode
72 and its associated
TFT
69. The pixel
4 (and the other pixels, and other TFT connections
such as gate leads, not shown, of the rest of the area of the glass plate
2
) constitute the display elements provided in the active matrix layer
14
and discussed earlier in relation to FIGS. 1 and 2.
In this embodiment, the glass plate is of thickness 1 mm, although any convenient
thickness may be used, and the various deposited layers are each of a thickness
between 0.05 mm and 1 micron, as per standard TFT manufacturing processes, except
for the second SiN layer
62 which in this example is 2 microns and the powderblast
resist layers
42 and
43. The powderblast resist layers
42
and
43 are discussed in more detail below The thickness of the second SiN
layer
62 defines the height of the acoustic chamber of the finished microphone,
so will in fact be chosen in part according to the required acoustic response properties
of the microphone. However, there is a trade-off with process costs in that thicker
layers take longer to produce, and furthermore in this embodiment there is a trade-off
with optimum TFT characteristics. Consequently, the thickness may be selected as
desired in the light of these trade-offs.
Unless otherwise stated, all the layers are deposited in conventional fashion,
and patterned and etched using standard photolithographic and etching techniques,
as described for example in U.S. Pat. No. 5,130,829. Any further details of the
parts of the display substrate
1 other than those related to the integrated
inclusion of the microphone
10, (i.e. the pixel
4, the other pixels
and gate leads and other external connections not shown, and other active matrix
components not shown, such as row and column address conductors) are likewise provided
and implemented in conventional fashion, again as described for example in U.S.
Pat. No. 5,130,829.
The powderblasting process carried out at step s
24 in the above process
is an example of powderblasting and is a known process for mechanically removing
solid material. Powderblasting, and powderblast resists, are discussed for example
in the reference H. J. Lighart , P. J. Slikkerveer, F. H. In't Veld, P. H. W. Swinkels
and M. H. Zonneveld, Philips Journal of Research, Vol. 50, No. 3/4 p.475-499 (1996).
Powderblasting is used for example to produce a rib-structure in the manufacture
of some types of plasma display panels.
In this embodiment the second powderblast resist layer
43 is subjected
to powderblasting throughout the powderblasting step s
24, and hence is required
to be a relatively strong and thick layer. The material used for the second powderblast
resist
43 is Ebecryl 270™, (available from UCB Chemicals, Netherlands),
which is a photosensitive elastomeric polymer based on polyurethane acrylate. This
comes in liquid form and is applied using a doctor blade, giving a thickness of
approximately 100 microns. This is patterned using photolithography. It will be
appreciated that other polymers or mask materials may be used instead.
The first powderblast resist layer
42 is however only exposed to powderblasting
toward the end of the powderblasting step s
24 when the powderblasting has
removed substantially all the thickness of the glass plate
2 in the cavity
28. It is therefore possible to use a thinner layer and/or weaker material
for the first powderblast resist layer
42, and hence in this embodiment
the material used is polyimide, and this is applied (at step s
4) by spin
coating to a few microns thickness and patterned using photolithography. This use
of a thin polyimide layer is particularly compatible with the thin layers subsequently
deposited thereon to form the microphone
10. As the polyimide is however
not of optimum resistance with respect to powderblasting, the powderblasting step
s
24 is preferably carefully timed so that the polyimide layer is only exposed
to the minimum powderblasting required to remove the glass from the cavity
28.
In other embodiments, such careful timing (or equivalent process control) may be
relaxed by employing a thicker and/or stronger material for the first powderblast
resist layer
42, for example by using the same material as used for the
second powderblast resist layer
43, although this provides a less compatible
layer thickness.
Also, in other embodiments, powders other than iron pellets, for example glass
beads, silica or alumina particles may be used. Also, other mechanical means for
removing the glass to form the cavity
28 may be used instead of powderblasting.
Instead of the glass plate
2, a plate of some other material may be
used, for example a quartz or plastic plate as used in some liquid crystal display
devices. A further possibility is a silicon plate, as used for example in so-called
liquid crystal on silicon (LCOS) display devices.
The process described above for forming the TFT
69 is a standard six-mask
bottom gate back channel etch, which provides an active matrix substrate for a
transmissive display. Alternatively, other types of TFT may be employed (e.g. top
gate, field shielded pixel, or bottom gate etch stop), some of which may use a
reduced mask count. Further, the display substrate may be for a reflective or transflective
display, rather than a transmissive display. Yet further, the invention may be
applied to other types of active matrix display substrates, for example ones using
thin film diodes as opposed to TFTs.
One particular advantage of the above embodiment is that all the layers used
to produce the microphone
10 are used in the formation of the TFT
69,
thus simplifying the overall production process. However, in other embodiments,
one or more of such layers may be deposited separately in the microphone area compared
to the TFT area so that the thickness and/or choice of material may be optimised
separately for the TFT and the microphone. This still advantageously shares process
flow aspects.
In other embodiments the microphone may instead be integrated on the passive
display
substrate, i.e. the glass plate
16 that has the common electrode
18
thereon, rather than the active display substrate. Although this shares less process
flow aspects, this will still provide, at least to a degree, the earlier described
advantages with respect to saving space etc. in an end product requiring a display
device and an acoustic transducer. Likewise, in other embodiments the microphone
may be integrated on a display substrate of a liquid crystal display device in
which both display substrates are of the passive type, i.e. a passive matrix liquid
crystal display.
It will be appreciated that the present invention may be also be applied to any
type of display device that includes a suitable display substrate. This includes,
inter alia, the following: a plasma display device; a field emission display device;
a polymer light emitting diode display device; and an organic light emitting diode
display device. In the case of a plasma display device, efficiencies in the production
process may be achieved if powderblasting is already used in the production process
of the plasma display device.
In the above embodiment the shape of the microphone as viewed from above the
glass
plate is substantially circular. Since the shape is merely defined by masks (i.e.
photoresist and powderblast resist) other shapes may be used as required, which
represents an advantage of the use of powderblasting.
Other types of microphone, for example an electret microphone, may be provided
instead of the condenser type microphone of the above embodiment.
The microphone provided in the above embodiment may also be used, i.e. constitute,
a speaker, if it is excited by application of an electrostatic field between the
two electrodes thereof. By varying the electrostatic field (i.e. by varying an
alternating voltage applied between the two electrodes) movement of the vibrating
diaphragm is achieved thus producing the required sound. In other embodiments,
a piezoelectric buzzer may be provided on the display substrate instead of a microphone.
In further embodiments, instead of a single acoustic transducer, more than one
acoustic transducer, comprising any combination of single or plural microphones,
speakers or piezoelectric buzzers, may be formed on the display substrate.
The thin film layers used for the display elements and the acoustic transducer(s)
may also be used to produce integral semiconductor circuitry required for operation
of the acoustic transducer.
In the main embodiment described above, processing efficiency is achieved by
virtue
of forming the display elements and the acoustic transducer in parallel as the
display substrate is built up on the glass plate. As already mentioned, if it is
desired to optimise one or more layers separately for the display elements or the
acoustic transducer, then individual layers may be deposited or processed separately
in the respective areas, with the other area either being masked from deposition
or having unnecessary layers removed therefrom. However, in some circumstances
overall production may be more efficient if the acoustic transducer and the display
elements are provided on the display substrate in quite separate processes, i.e.
the display elements are formed first, and then the acoustic transducer, or vice-versa.
This may be the case, for example, where a standard design of display area is required
to be combined with various types, numbers, sizes, or positions of acoustic transducers.
Furthermore, discrete acoustic transducers may be provided by forming
just the acoustic transducer part of the above embodiments, without display elements.
Further embodiments that are particularly suited to separate formation of
the acoustic transducer will now be described with reference to FIGS. 5 to
7.
It will be appreciated that, in the same way as with the embodiments of FIGS. 1
to
4, the embodiments of FIGS. 5 to
7 allow the provision of acoustic
transducers on display substrates (with display elements added either previously
or afterwards), as well as the provision of separate discrete acoustic transducers
by forming just the acoustic transducer part to be described, without display elements.
FIG. 5 shows the process steps employed in a further condenser microphone embodiment.
These process steps will now be described, with the aid of FIGS. 6
a and
6b which schematically illustrate the build-up of the features of
the microphone.
The features shown in FIG. 6
a are formed as follows. At step s
40,
a glass plate
102, of thickness 0.7 mm, is provided. At step s
42
a bottom powderblast resist layer
104 is deposited on the bottom surface
of the glass plate
102 and patterned with a gap
105 in the area corresponding
to where the microphone is to be provided, and a top powderblast resist layer
106
is deposited on the top surface of the glass plate
102. In this embodiment,
both the powderblast resist layers
104,
106 are of Ebecryl 270™
(available from UCB Chemicals, Netherlands) which was discussed earlier in relation
to the first main embodiment, and of a thickness of about 100 microns. Furthermore,
in the present embodiment, the possibilities and influences of the choice of powderblast
resist are the same as in the first main embodiment. At step s
44, various
layers are successively deposited on the top surface of the glass plate
102,
each to a thickness of between 0.05 mm and 1 microns (but as in the other embodiments,
the thicknesses may of course be varied as required). The layers are, in order
of deposition, a first SiN layer (i.e. insulating layer)
108, a bottom chromium
layer
110 (to serve as a conductor), an aluminium layer
112 (which
will serve as a sacrificial layer), a second SiN layer (i.e. insulating layer)
114, and a top chromium (or other metal) layer
116 (to serve as a
conductor). Thus the overall structure shown in FIG. 6
a is arrived at.
The additional features shown in FIG. 6
b are formed as follows. At step
s
46, powderblasting is performed to provide a cavity
120 is provided
in the glass plate, extending the whole depth of the glass plate
102, in
the area where the diaphragm of the microphone is to be provided. At step s
48,
various layers are removed in selected areas i.e. the remaining powderblast resist
from the top powderblast resist layer
106 at the area of the cavity
120;
the sacrificial aluminium layer
112 in this area; and selected areas in
the second SiN layer
114 and the top metal layer
116 (for providing
acoustic air holes and electrical contacts to underlying layers). This results
in a completed microphone
130, comprising a vibrating diaphragm
122
(the vibrating diaphragm
122 comprising the first SiN layer
108 and
the bottom chromium layer
110 in the area over the cavity
120), a
fixed electrode structure
124 (the fixed electrode structure
124
comprising the top metal layer
116 and the second SiN layer
114 in
the area over the diaphragm
122, and further comprising acoustic air holes
129 therein), a contact
128 for the fixed electrode and a contact
126 for the vibrating electrode.
As described with respect to the microphone of the first main embodiment, the
structure of FIG. 6
b may also be used to provide a speaker rather than a microphone.
In all of the above embodiments, the cavity over which the vibrating diaphragm
is located is formed by removing material from the glass plate (e.g. glass plate
2 or glass plate
102). In other embodiments, the cavity may be formed
instead by providing one or more sacrificial layers between the glass plate and
the layers that will form the vibrating diaphragm, then removing the sacrificial
layer(s) to produce the cavity in the space vacated by the sacrificial layer(s).
Any appropriate material may be used for the sacrificial layer(s), including for
example SiN, Al, or organic material such as photoresist.
In a further embodiment, an acoustic transducer comprising a piezoelectric buzzer,
schematically illustrated in FIG. 7
a, is provided. The piezoelectric buzzer
201 comprises a glass plate
202 with a cavity
204, of rectangular
area, sized as required for acoustic properties, in this example approximately
10 mm×10 mm, formed therein by powderblasting such as to extend through the
whole depth of the glass plate
202.
A square shaped plate of piezoelectric material
206, in this embodiment
lead zircanoate titanate (PZT) of thickness as required for acoustic properties,
in this example of the order of 100 microns, and of approximate area 10 mm×10
mm, is provided with electrodes
208 and
210 on the top and bottom
surfaces thereof. The plate of piezoelectric material
206 is bonded to the
glass plate
202, over the cavity
204, thereby providing the piezoelectric
transducer
201. In this embodiment the plate of piezoelectric material
206
is bonded to the glass plate
202 along substantially the whole of the perimeter
of its square area, thereby forming a diaphragm.
The plate of piezoelectric material
206 may alternatively be made slightly
smaller than the area of the cavity
204, and bonded along only one side
thereof, thereby forming a cantilever, as shown in FIG. 7
b.
The diaphragm or cantilever may alternatively be provided over a cavity
212,
again produced by powderblasting, that differs from the cavity
204 in that
it only extends through some of the depth of the glass plate
202, as shown
in FIG. 7
c (for the diaphragm) and FIG. 7
d (for the cantilever).
The plate of piezoelectric material
206 with electrodes thereon may conveniently
be provided by applying a plurality of electrodes over respective areas of a larger
sheet of piezoelectric material and then cutting the processed sheet into individual
electrode coated plates
206.
The cavity
204,
212 and plate of piezoelectric material
206
may be formed in shapes other than square.
The piezoelectric buzzer
201 is operated by applying an alternating voltage
between the two electrodes
208,
210.
It will be appreciated that the above examples of provision of display substrates
(e.g. liquid crystal display substrates) and acoustic transducers (e.g. microphones)
are described by way of example only, and that the invention may be applied to
the provision of any other appropriate type of display substrate and/or acoustic
transducer. Likewise, layer characteristics, such as type of material and thickness,
are merely exemplary.
From reading the present disclosure, other variations and modifications will
be apparent to persons skilled in the art. Such variations and modifications may
involve equivalent and other features which are already known in the design, manufacture
and use of display devices and acoustic transducers, and which may be used instead
of or in addition to features already described herein.
Although Claims have been formulated in this Application to particular combinations
of features, it should be understood that the scope of the disclosure of the present
invention also includes any novel feature or any novel combination of features
disclosed herein either explicitly or implicitly or any generalisation thereof,
whether or not it relates to the same invention as presently claimed in any Claim
and whether or not it mitigates any or all of the same technical problems as does
the present invention. Features which are described in the context of separate
embodiments may also be provided in combination in a single embodiment. Conversely,
various features which are, for brevity, described in the context of a single embodiment,
may also be provided separately or in any suitable subcombination. The Applicants
hereby give notice that new Claims may be formulated to such features and/or combinations
of such features during the prosecution of the present Application or of any further
Application derived therefrom.
*
