Title: Thermo pile infrared ray sensor manufactured with screen print and method thereof
Abstract: In a thermo pile infrared ray sensor, an opening portion is formed by etching a substrate from a second surface after an n-type poly-Si layer and a thin aluminium layer are formed so that first and second connection portions are formed by parts thereof. An infrared ray absorbent layer is formed on the substrate to cover the first connection portion with a screen print after the opening portion is formed.
Patent Number: 6,870,086 Issued on 03/22/2005 to Hamamoto, et al.
| Inventors:
|
Hamamoto; Kazuaki (Nagoya, JP);
Yoshida; Takahiko (Okazaki, JP);
Suzuki; Yasutoshi (Okazaki, JP);
Toyoda; Inao (Anjo, JP)
|
| Assignee:
|
Denso Corporation (Kariya, JP);
Nippon Soken, Inc (Nishio, JP)
|
| Appl. No.:
|
164603 |
| Filed:
|
June 10, 2002 |
Foreign Application Priority Data
| Jun 11, 2001[JP] | 2001-176138 |
| Jul 16, 2001[JP] | 2001-215183 |
| Nov 06, 2001[JP] | 2001-341066 |
| Current U.S. Class: |
136/225; 427/58 |
| Intern'l Class: |
H01L 035//28; B05D 005//12 |
| Field of Search: |
136/224,225
427/58
|
References Cited [Referenced By]
U.S. Patent Documents
| 6348650 | Feb., 2002 | Endo et al. | 136/201.
|
| 6720559 | Apr., 2004 | Kubo | 250/338.
|
| Foreign Patent Documents |
| B2-55-17104 | May., 1980 | JP.
| |
| B2-57-29683 | Jun., 1982 | JP.
| |
| A-62-222134 | Sep., 1987 | JP.
| |
| A-5-231926 | Sep., 1993 | JP.
| |
| A-5-231946 | Sep., 1993 | JP.
| |
| A-6-109535 | Apr., 1994 | JP.
| |
| A-9-133578 | May., 1997 | JP.
| |
| A-2000-340848 | Dec., 2000 | JP.
| |
Primary Examiner: Ryan; Patricia
Assistant Examiner: Parsons; Thomas H.
Attorney, Agent or Firm: Posz & Bethards, PLC
Claims
What is claimed is:
1. A manufacturing method for a thermo pile infrared ray sensor comprising:
preparing a substrate having first and second surfaces;
forming a first material layer dividing several parts on the first surface
of the substrate with a first conductive material;
forming a second material layer having several parts with a second
conductive material different from the first conductive material to form
first and second connection portions with the several parts of the first
material layer;
forming one of an opening portion and a depressed portion by etching the
substrate from the second surface where the first connection portion is
formed; and
screen printing a carbon paste mixed with a polyester resin including
carbon particles to form an infrared ray absorbent layer on the substrate
to cover the first connection portion after the forming one of the opening
portion and a depressed portion.
2. A method for manufacturing a thermo pile infrared ray sensor according
to claim 1,
wherein the screen printing the infrared ray absorbent layer includes
screen printing the infrared ray absorbent layer so that a size ratio of a
width of one of the opening and the depressed portion to a width of the
infrared ray absorbent layer is 0.75 to 0.90.
3. A manufacturing method for a thermo pile infrared ray sensor comprising:
preparing a substrate having first and second surfaces;
forming a first material layer dividing several parts on the first surface
of the substrate with a first conductive material;
forming a second material layer having several parts with a second
conductive material different from the first conductive material to form
first and second connection portions with the several parts of the first
material layer;
forming one of an opening portion and a depressed portion by etching the
substrate from the second surface where the first connection portion is
formed; and
screen printing an infrared ray absorbent layer on the substrate to cover
the first connection portion after the forming one of the opening portion
and a depressed portion, wherein
the screen printing of the infrared ray absorbent layer includes screen
printing the infrared ray absorbent layer so that a pressure applied on
the substrate is at most 0.25 MPa.
4. A manufacturing method for a thermo pile infrared ray sensor comprising:
preparing a substrate having first and second surfaces;
forming a first material layer dividing several parts on the first surface
of the substrate with a first conductive material;
forming a second material layer having several parts with a second
conductive material different from the first conductive material to form
first and second connection portions with the several parts of the first
material layer;
forming one of an opening portion and a depressed portion by etching the
substrate from the second surface where the first connection portion is
formed; and
screen printing a carbon paste with a carbon addition ratio that is at
least 20 wt % and mixed with a polyester resin including carbon particles
to form an infrared ray absorbent layer on the substrate to cover the
first connection portion after the forming of one of the opening portion
and a depressed portion.
5. A manufacturing method for a thermo pile infrared ray sensor comprising:
preparing a substrate having first and second surfaces;
forming a first material layer dividing several parts on the first surface
of the substrate with a first conductive material;
forming a second material layer having several parts with a second
conductive material different from the first conductive material to form
first and second connection portions with the several parts of the first
material layer;
forming one of an opening portion and a depressed portion by etching the
substrate from the second surface where the first connection portion is
formed; and
screen printing a carbon paste with a carbon addition ratio that is 30 to
60 wt % and mixed with a polyester resin including carbon particles to
form an infrared ray absorbent layer on the substrate to cover the first
connection portion after the forming one of the opening portion and a
depressed portion.
6. A manufacturing method for a thermo pile infrared ray sensor comprising:
preparing a substrate having first and second surfaces;
forming a first material layer dividing several parts on the first surface
of the substrate with a first conductive material;
forming a second material layer having several parts with a second
conductive material different from the first conductive material to form
first and second connection portions with the several parts of the first
material layer;
forming one of an opening portion and a depressed portion by etching the
substrate from the second surface where the first connection portion is
formed; and
screen printing an infrared ray absorbent layer on the substrate so that a
center line average roughness thereof is at least 0.5 .mu.m to cover the
first connection portion after the forming of one of the opening portion
and a depressed portion.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of Japanese Patent
Application No. 2001-176138 filed on Jun. 11, 2001, No. 2001-215183 filed
on Jul. 16, 2001, and No. 2001-341066 filed on Nov. 6, 2001, the contents
of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to a thermo pile infrared ray sensor and
manufacturing method thereof having an infrared ray absorbent layer that
absorbs infrared rays thereon.
DESCRIPTION OF THE RELATED
In a conventional infrared ray sensor, a gold-black layer made of gold
ultra-fine particles having a high infrared ray absorbency ratio or carbon
layer is usually adopted as an infrared ray absorbent material that
absorbs infrared rays and exchanges the absorbed rays into heat. For
example, JP-B-55-17104 discloses a manufacturing process of a gold-black
layer formed by depositing gold on a substrate at 0.1 Torr in as Argon gas
atmosphere using a vacuum deposition apparatus and repeatedly depositing
gold on the substrate at 1 Torr in the Argon gas atmosphere. On the other
hand, JP-A-6-108535 discloses a manufacturing process of a carbon layer
having a high infrared ray absorbency ratio and formed by resolving carbon
hydride (e.g., methane, ethylene or acetylene) using vacuum glow
discharging.
In JP-B-55-17104, to obtain a high adhesion strength of the conventional
gold-black layer, the depositing of the gold is conducted twice. However,
the resulting durability of the adhesion strength of the gold-black layer
is insufficient. Further, the manufacturing cost of the gold-black layer
increases because the manufacturing process is complex.
To the contrary, JP-B-57-29683 also discloses a manufacturing process of
the gold-black layer. That is, a gold-black layer having a two-layer
construction is formed by spraying carbon particles onto a substrate to
form a foundation and then depositing the gold-black layer. However, the
resulting durability of the adhesion strength of the gold-black layer is
insufficient, too. Also, the manufacturing cost of the gold-black layer
increases for the same reason as mentioned above.
The gold-black layer and the carbon layer formed by the above-mentioned
manufacturing process are etched by photo lithography to pattern
predetermined shape. Therefore, the manufacturing cost of the gold-black
layer further increases because specialized equipment is required for the
photolithography process such as, for example, a photolithography machine
and a dry etching machine.
Further, in the manufacturing process disclosed in JP-A-6-109535, an
infrared ray sensor diaphragm is formed to decrease thermal capacitance
formed by the substrate and the infrared ray absorbent layer after the
carbon layer is formed. However, the infrared ray sensor may be
contaminated by carbon included in the infrared ray absorbent layer during
the formation of the diaphragm.
Generally, a thermo pile infrared ray sensor includes a membrane formed in
a thick portion of a substrate, a thermoelectric couple having a warm
connection portion formed on the membrane and a cold connection portion
formed on the periphery of the membrane, and an infrared ray absorbent
layer formed on the membrane to cover the warm connection portion. The
thermo pile infrared ray sensor detects infrared rays based on a voltage
change generated between the thermoelectric couple when the infrared rays
are irradiated thereon.
However, a thermo pile infrared ray sensor voltage is typically low.
Specifically, a distance between the warm and cold portions of the
thermoelectric couple, or heat separation width is often too large, or the
membrane is too thick, to reduce the heat capacitance of the warm
connection portion necessary to obtain a large voltage output because heat
from the warm connection portion cannot easily escape and the temperature
difference between the warm and cold connection portions of the
thermoelectric couple becomes large.
Therefore, the substrate area must be increased to lengthen the heat
separation width, or membrane material changes must be made to enable the
heat to escape from the warm connection portion, thereby increasing the
manufacturing cost of such a device.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a
manufacturing method for a thermo pile infrared ray sensor that obviates
the above limitations.
It is another object of the present invention to provide a manufacturing
method for a thermo pile infrared ray sensor that enables such a sensor to
be manufactured at a low cost.
It is another object of the present invention to provide a thermo pile
infrared ray sensor that obtains an appropriately output signal without a
lengthened sensor tip.
In a thermo pile infrared ray sensor of the present invention, one of an
opening portion and a depressed portion is formed by etching a substrate
from a second surface after first and second material layers are formed so
that a first and a second connection portions are formed based on parts of
the first and second material layers. An infrared ray absorbent layer is
formed on the substrate to cover the first connection portion with a
screen print after one of the opening portion and a depressed portion is
formed.
According to the infrared ray sensor of the present invention, the infrared
ray absorbent layer cannot peel from the substrate because it is formed
after the etching for the opening portion is performed. Therefore, a
complex process that prevents the infrared ray absorbent layer from
peeling is not needed, and the infrared ray sensor can be manufactured at
a low cost.
In a thermo pile infrared ray sensor of the present invention, the infrared
ray absorbent layer is formed so that a size ratio of a width of one of
the opening and the depressed portion to a width of the infrared ray
absorbent layer is 0.75 to 0.90.
According to the infrared ray sensor of the present invention, it is
possible to increase sensor output without lengthening the sensor tip.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects, features and advantages of the present invention will be
understood more fully from the following detailed description made with
reference to the accompanying drawings. In the drawings:
FIG. 1 is a front view showing a thermo pile infrared ray sensor according
to a first embodiment of the present invention;
FIG. 2 is a cross sectional view taken along line IIB--IIB of FIG. 1;
FIG. 3 is cross sectional view showing production processes of the thermo
pile infrared ray sensor according to the first embodiment;
FIG. 4 is cross sectional view showing production processes of the
electrical capacitance pressure sensor following FIG. 3;
FIG. 5 is cross sectional view showing production processes of the
electrical capacitance pressure sensor following FIG. 4;
FIG. 6 is cross sectional view showing production processes of the
electrical capacitance pressure sensor following FIG. 5;
FIG. 7 is a schematic view showing a carbon paste print process according
to the first embodiment;
FIG. 8 is a graph showing a relationship between applied pressure during
screen printing and a membrane damage generation ratio;
FIGS. 9A and 9B are front views showing print conditions of polyester resin
paste and phenol resin paste;
FIG. 10 is a line graph showing a relationship between a carbon addition
ratio and an infrared ray transmission ratio;
FIG. 11 is a line graph showing a relationship between surface roughness
and a reflection ratio;
FIG. 12 is a line graph showing a relationship between a carbon addition
ratio and surface roughness;
FIG. 13 is a line graph showing a relationship between a carbon addition
ratio and an infrared ray absorbency ratio;
FIG. 14 is a cross sectional view showing a thermo pile infrared ray sensor
of a second embodiment of the present invention;
FIG. 15 is a cross sectional view showing a thermo pile infrared ray sensor
of the second embodiment;
FIG. 16 is a front view showing a thermo pile infrared ray sensor according
to a third embodiment of the present invention;
FIG. 17 is a cross sectional view taken along line XVIIB--XVIIB of FIG. 16;
and
FIG. 18 is a line graph showing relationships between Lb/La and output
error and between Lb/La and thermo pile output.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will be described further with reference to various
embodiments shown in the drawings.
First Embodiment
Referring to FIGS. 1 and 2, a thermo pile infrared ray sensor (infrared ray
sensor) is manufactured based on substrate 1. The substrate 1 is, for
example, semiconductor substrate such as a single-crystal silicon
substrate having a thickness of 400 .mu.m and has a first surface 1a
(upper surface in FIG. 2) and a second surface 1b (lower surface in FIG.
2). A surface direction of the first surface 1a is, for example, (100)
plane or (110) plane. An opening portion 2 is formed in the substrate 1 to
penetrate from the second surface 1b to the first surface 1a in a
direction perpendicular to the substrate 1 by anisotropic etching. Length
and breadth sizes (widths) of the opening portion 2 are approximately 1
mm.
Isolation layers 3, 4, 5 are formed on the first surface 1a of the
substrate 1 to cover the opening portion 2. The isolation layer 3, 5 are
made of silicon nitride and the isolation layer 4 is made of silicon
oxide. The isolation layers 3-5 are respectively formed by CVD, sputter
deposition or the like. The total thickness of the isolation layers 3-5
is, for example, 2 .mu.m.
A poly-Si layer 6 doped with n-type impurities (n-type poly-Si layer) is
formed by CVD or the like and is patterned on the isolation layers 3-5. An
isolation layer 7 and a thin aluminum layer 8 are formed on the isolation
layers 3-5 and the n-type poly-Si layer 6 by sputter deposition or the
like. Contact holes 7a are formed in the isolation layer 7 through which
the thin aluminum layer 8 and the n-type poly-Si layer 6 are contacted
with each other. Specifically, parts of the thin aluminum layer and parts
of the poly-Si layer 6 are alternatively patterned and respective parts
are directly contacted with each other at both ends or one end thereof to
form strip-shaped sensing wiring.
A passivating layer 9, which is made of a silicon oxide layer, TEOS layer
or the like, is formed on the thin aluminium layer 8. An infrared ray
absorbent layer 10 made of carbon is formed on a predetermined region of
the passivating layer 9. For example, a thickness of the infrared ray
absorbent layer 10 is approximately 6 .mu.m and length and breadth sizes
(widths) Lb of the infrared ray absorbent portion 10 are approximately 0.8
mm respectively.
The infrared ray absorbent layer 10 is rectangularly shaped and is arranged
on the center of the substrate 1. First connection portions 11 of the
n-type poly-Si layer 6 and the thin aluminium layer 8 are positioned under
the infrared ray absorbent layer 10, while second connection portions 12
of the n-type poly-Si layer 6 and the thin aluminium layer 8 are
positioned on the periphery of the infrared ray absorbent layer 10. That
is, the second connection portions 12 are not positioned under the
infrared ray absorbent layer 10.
As shown in FIG. 1, a first terminal 13 and a second terminal 14 are formed
on the isolation layers 3-5. The first and second terminals 13, 14
respectively connect to ends of the series circuit formed by the n-type
poly-Si layer 6 and the thin aluminium layer 8.
In this construction, a temperature of the first connection portions 11
increases when the infrared ray absorbent layer 10 absorbs infrared rays
because the n-type poly-Si layer 6 and the thin aluminium layer 8 are
different materials. Therefore, the first connection portions 11
positioned on the opening portion 2 and the second connection portions 12
positioned on the substrate 1 around the opening portion 2 construct
thermoelectric coupling groups having Seebeck coefficient. The first
connection portions 11 correspond to warm connection portions and the
second connection portions 12 correspond to cold connection portions.
Also, in this construction, sensor elements Es shown in FIG. 2 are formed
on a membrane having a thin layer and formed on the opening portion 2 of
the substrate 1. Therefore, a heat capacitance of the first connection
portions 11 is smaller than that of the second connection portions 12
formed on the substrate 1 except at the opening portion 2 because the
substrate 1 acts a heat sink.
In the present infrared ray sensor, the infrared absorbent layer 10 absorbs
and generates heat when infrared rays are incident thereon. The heat
changes into an electromotive force between the thermoelectric couples. In
detail, when the infrared absorbent layer 10 absorbs infrared rays emitted
from a human body or the like, a temperature thereof increases. As a
result, a temperature of the first connection portion 11 under the
infrared absorbent layer 10 also increases. On the other hand, a
temperature of the second connection portion 12 does not increase because
the substrate 1 acts heat sink. Accordingly, a temperature difference is
generated between the first and second connection portions 11, 12, and the
electromotive force is, therefore, generated therebetween based on the
Seebeck effect.
The electromotive force is detected from the first and second terminals 13,
14 of the series circuit as a sensor output signal Vout. Accordingly,
infrared rays can be detected based on the electromotive force and a
temperature of the human body or the like that generates the infrared
rays. Incidentally, the electromotive force to be generated depends on the
number of the thermoelectric couples. Accordingly, in the present
embodiment, the number of the thermoelectric couples is set in a range
from several dozen to hundreds to increase the sensor output.
A manufacturing process of the infrared ray sensor of the present
embodiment is described with reference to FIGS. 3-6. FIGS. 3-6, which each
show a cross sectional view of apart of the infrared ray sensor
corresponding to FIG. 2.
First, as shown in FIG. 3, a silicon wafer having first and second surfaces
1a, 1b is prepared as the substrate 1. The isolation layers 3-5 are formed
on the first surface 1a of the substrate 1. Next, a silicon nitride layer
20 is formed on the second surface 1b of the substrate 1 as a mask to form
the opening portion 2. A window portion 21 is then formed in the silicon
nitride layer 20. The n-type poly-Si layer 6 is formed and patterned on
the isolation layers 3-5 and the isolation layer 7 and the thin aluminium
layer 8 is further formed and patterned thereon. The passivating layer 9
is formed on the thin aluminium layer 8 to cover respective elements of
the infrared ray sensor.
Here, a total thickness (t) of the respective elements 3-9 is, for example,
set approximately at 1.5 to 2.8 .mu.m so as not to deform after the
opening portion 2 is formed.
As shown in FIG. 4, a protection layer 30 made of organic resin (resist
material) is formed on a side of the first surface 1a of the substrate 1
to protect against etching liquid. Next, the opening portion 2 is formed
in the substrate 1 by anisotropic etching through the silicon nitride
layer 20. For example, the substrate 1 is immersed into alkali etching
liquid such a potassium hydroxide solution. An etching amount is
controlled based on an etching time and the etching is stopped when the
silicon positioned at the opening portion is removed.
As shown in FIG. 5, the etching protection layer 30 is removed. In this
case, the infrared ray absorbent layer 10 has not been formed yet.
Subsequently, as shown in FIG. 6, the infrared ray absorbent layer 10 is
formed on a predetermined region of the passivating layer 9 by screen
printing carbon paste and drying it. The screen printing is described with
reference to FIG. 7.
In the present embodiment, an off contact type of screen printing is
employed. A screen 41 installed in a screen frame 42 disposed above the
wafer 40 and is slightly separated from a surface of the wafer 40. The
screen 41 has a predetermined window portion. A carbon paste 43 is mounted
on the screen 41 and is squeezed out from the window portion of the screen
41 by moving a squeezer 44 on the screen 41 with a predetermined squeezing
pressure. Here, the squeezing pressure F3 applied on the wafer 40 (i.e.,
substrate 1) is at most 0.25 Mpa. This is because the respective elements
3-9 of the infrared ray sensor may be destroyed due to the squeezing
pressure.
A polyester resin mixed with carbon particles is mixed with the carbon
paste 43 to be used for the screen print. Specifically, a diameter of the
carbon particles is approximately 2 to 3 .mu.m to increase an infrared ray
absorbency ratio, and a carbon addition ratio of the polyester resin is at
least 20 wt %, and preferably 30 to 60 wt % to decrease an average surface
roughness Ra of the infrared ray absorbent layer 10 at least 0.5 .mu.m.
After screen printing, the substrate 1 is accommodated into a heater and is
dried. Therefore, the infrared ray absorbent layer 10 is formed.
Successively, the substrate 1 is separated by a dicing cutter, thereby
completing the infrared ray sensor of the present embodiment.
The reasons for utilizing the numeric values of the squeeze pressure, the
diameter of the carbon particle, the carbon dopant ratio of the polyester
resin and the average surface roughness Ra are described with reference to
FIGS. 8-13.
FIG. 8 shows investigation results regarding the above described screen
printing. A horizontal axis shows pressure F3 applied to the substrate 1
during the screen printing, and a longitudinal axis shows a membrane
damage generation ratio. The pressure F3 is equal to downward force
expressed with a value that is equal to a squeezer pressure F1 subtracted
from a restitution force F2, where the squeezer pressure F1 is a pressure
force applied the screen 41 by the squeezer 44 and the restitution force
F2 is an elastic force of the screen 41 for becoming restored to its
original state. In this investigation, a thickness of the membrane t
(i.e., total thickness of the respective layers 3-9) is 1.5 to 2.8 .mu.m
and the Length and breadth sizes of the opening portion 2 are
approximately 1 mm respectively.
Referring to FIG. 8, it can be understood that the membrane damage
generation ratio considerably increases when the pressure F3 during the
screen print is 0.25 MPa or more. Therefore, it is preferable to set the
pressure applied to the substrate 1 (membrane) to at most 0.25 MPa during
the formation of the infrared ray absorbent layer 10.
FIGS. 9A and 9B show print conditions when a polyester resin paste that is
a polyester resin including carbon particles and a phenol resin paste that
is a phenol resin including carbon particles are printed. An average
diameter of the added carbon particles is 2 to 3 .mu.m to increase an
infrared ray absorbency ratio. Referring to FIGS. 9A and 9B, it is evident
that the polyester resin paste is superior to the phenol resin paste for
screen printing purposes.
When a patterning of the screen print is conducted with a paste including a
phenol resin (or a polyamide resin, a polyimide resin, an epoxy resin, or
an acrylic resin) including with carbon particles (graphite), painting
performance and adhesiveness to glass family materials such as silicon
family layers including a TEOS layer or the like that are used for the
surface of the infrared ray sensor are not good. That is, a patterned
shape of the printed paste is not good if length and breadth sizes thereof
are 1 mm respectively, which is the same as that of the infrared ray
absorbent layer 10.
To the contrary, in this present embodiment, a polyester resin having good
painting performance and an adhesiveness to glass family materials that
are used for surface of the infrared ray sensor is employed to material of
the infrared ray absorbent layer 10 formed by screen printing. Also,
carbon is added to the polyester resin paste to increase the infrared ray
absorbency ratio. Therefore, it is possible to form the infrared ray
absorbency layer having a high infrared ray absorbency ratio and good
resulting printed shape and at low cost.
The infrared ray absorbency ratio, the infrared ray transmission ratio and
an infrared ray reflection ratio in sum equal 100%. Accordingly, it is
necessary that the infrared ray transmission ratio and the infrared ray
reflection ratio decrease to increase the infrared ray absorbency ratio.
FIG. 10 shows a relationship between a carbon addition ratio and the
infrared ray transmission ratio. Referring to FIG. 10, as the carbon
addition ratio in the paste increases, the infrared ray transmission ratio
decreases. This is because the percentage of infrared rays absorbed by the
carbon increases. Especially, the infrared ray transmission ratio
considerably decreases if the carbon addition ratio is at least 20 wt %.
FIG. 11 shows a relationship between surface roughness (center line average
roughness Ra: JIS B0601-1994) of the infrared ray absorbent layer and the
infrared ray reflection ratio thereof. The infrared ray reflection ratio
decreases as the surface roughness increases because multiple reflections
on the surface of the infrared ray absorbent layer 10 increase.
Especially, the infrared ray reflection ratio is at most 10% when the
surface roughness is at least 0.5 .mu.m.
FIG. 12 shows a relationship between the carbon addition ratio and the
surface roughness. Referring to FIG. 12, the surface roughness changes
based on the carbon addition ratio. The surface roughness is at least 0.5
.mu.m when the carbon addition ratio is at least 20 wt %. Accordingly, the
infrared ray reflection ratio can be lower when the carbon addition ratio
is at least 20 wt %.
However, the surface roughness decreases if the carbon addition ratio is
further increased because spaces between the carbon particles are
shortened as a density of the carbon in the infrared ray absorbent layer
10 increases. Therefore, it is preferable that the carbon addition ratio
is not too high.
FIG. 13 shows a relationship between the carbon addition ratio and the
infrared ray absorbency ratio. In the present investigation, a wavelength
of the infrared ray is 10 .mu.m. A thickness of the infrared ray absorbent
layer 10 is at least 3 .mu.m because an absorbent performance of an
electromagnetic wave absorber increases when its thickness is at least one
quarter of the electromagnetic wavelength.
Referring to FIG. 13, high infrared ray absorbency ratio can be obtained
when the carbon addition ratio is at least 20 wt %. Especially, the
infrared ray absorbency ratio is at least 90% when the carbon addition
ratio is 30 to 60 wt %.
According to the present embodiment, it is possible to manufacture the
infrared ray sensor at low cost without using expensive equipment such as
a vacuum deposition apparatus, a photolithography machine and a dry
etching machine. Also, an infrared ray absorbent layer 10 having a high
infrared ray absorbency ratio and good pattern shape can be formed.
As mentioned above, the infrared ray sensor of the present embodiment has
features as follows.
The opening portion 2 is formed by etching from the second surface 1b of
the substrate 1 (FIG. 3) after the n-type poly-Si layer 6 and the thin
aluminium layer 8 are formed on the first surface 1a of the substrate 1
(FIG. 4). The infrared ray absorbent layer 10 is then formed on the side
of the first surface 1a of the substrate 1 with screen paint (FIG. 6).
In the case that the opening portion 2 is formed after the infrared ray
absorbent layer 10 is formed, the infrared ray absorbent layer 10 may peel
from the substrate 1 when the protection layer 30 (FIG. 4) is removed.
However, according to the present embodiment, the infrared ray absorbent
layer 10 cannot peel from the substrate 1 because it is formed after the
etching for the opening portion 2. Therefore, a complex manufacturing
process required to prevent peeling of the infrared ray absorbent layer 10
is not needed, and the infrared ray sensor can be manufactured with low
cost.
Forming processes of the n-type poly-Si layer 6 and the thin aluminium
layer 8 and an etching process for the opening portion 2 is practiced in a
clean room, while a forming process of the infrared ray absorbent layer 10
is practiced outside of the clean room.
In the case that the respective processes mentioned above are practiced in
the clean room, the clean room is polluted by the forming process of the
infrared ray absorbent layer 10. However, the present embodiment can
prevent the clean room from being polluted because the infrared ray
absorbent layer 10 is formed outside of the clean room via screen
printing.
During screen printing, a pattern shape of the infrared ray absorbent layer
10 is formed on the screen 41. That is, the infrared ray absorbent layer
10 is simultaneously completed when the screen printing is conducted.
Accordingly, a photolithography machine and dry etching machine for
patterning an infrared ray absorbent layer 10 formed by vacuum deposition
is not needed in the present embodiment. Therefore, the infrared ray
absorbent layer 10 can be formed by a screen printing machine that is less
expensive than a vacuum deposition apparatus, and therefore the infrared
ray sensor can be manufactured at low cost.
The squeezing pressure to be applied to the substrate 1 during the screen
printing is at most 0.25 MPa. Therefore, it is preferable to form the
infrared ray absorbent layer 10 after etching to avoid damaging the
membrane.
The carbon paste 43 made of polyester with carbon particles is used for
forming the infrared ray absorbent layer 10. Therefore, the infrared ray
absorbent layer 10 can be formed with a accurate print shape. Also, the
carbon addition ratio of the carbon paste 43 is at least 20 wt %
(preferably 30 to 60 wt %). Therefore, the infrared ray absorbent layer 10
can be formed with a high infrared ray absorbency ratio. Further, the
surface roughness of the infrared ray absorbent layer 10 is at least 0.5
.mu.m. Therefore, the infrared ray absorbent layer 10 can be formed with a
low infrared ray reflection ratio. Accordingly, when carbon paste made of
polyester with carbon particles whose carbon addition ratio is 30 to 60 wt
%, and when the surface roughness of the infrared ray absorbent layer 10
at least 1 .mu.m and its thickness is at least 3 .mu.m, it is possible to
form the infrared ray absorbent layer 10 having an infrared ray absorbency
ratio of at least 90%.
Second Embodiment
In the second embodiment shown in FIGS. 14 and 15, a thermo pile infrared
ray sensor (infrared ray sensor) has a different construction from the
first embodiment. As shown in FIG. 14, in this embodiment, the infrared
ray sensor is modified with respect to that in the first embodiment.
In the infrared ray sensor, a depressed portion 50 is formed in the
substrate 1. That is, a diaphragm 51 is formed in the substrate 1 on which
the first connection portions 11 of the thermoelectric couples are formed.
In this case, as shown in FIG. 15, an etching process for the depressed
portion 50 is stopped before the etching proceeds through the first
surface 1a of the substrate 1. Incidentally, a thickness of the diaphragm
51 is definable. It is, however, preferably as thin as possible because
the thermo capacitance of the diaphragm 51 decreases as the thickness
thereof decreases and a temperature difference between the first and
second connection portions 11, 12 increases.
Third Embodiment
In the third embodiment shown in FIGS. 16 and 17, sizes of the membrane and
the infrared ray absorbent layer 10 are determined to obtain a larger
output Vout of the thermo pile infrared ray sensor (infrared ray sensor)
than that of the first embodiment.
Specifically, a ratio (size ratio) of Lb/La is determined to preferably be
in a range of 0.75 to 0.90. In the infrared ray sensor, it is necessary to
increase a temperature difference between the first and second connection
portions 11, 12 to enlarge the sensor output Vout. The temperature
difference T is shown in Equation (1) where the thermo resistance between
the first and second connection portions 11, 12 is R, an infrared ray
energy applied to the infrared ray sensor is I, the total area of the
infrared ray absorbent layer 10 is S.
T=RIS (1)
According to Equation (1), the temperature difference T can be enlarged by
increasing the thermo resistance R (i.e., thermo separate distance) or by
increasing the size of the infrared ray absorbent layer 10. The size of
the infrared ray absorbent layer 10 decreases as the thermo resistance R
increases. On the other hand, the thermo resistance R decreases as the
size of the infrared ray absorbent layer 10 increases. Therefore, the
sensor output Vout can be enlarged based on the ratio of Lb/La.
FIG. 18 shows results of a finite element modeling (FEM) analysis on a
change of the sensor output Vout when the ratio Lb/La is altered. In this
case, the ratio Lb/La is altered by altering the sizes Lb of the infrared
absorbent layer 10 while maintaining the sizes La of the membrane (layers
3-9). The analysis is executed based on a temperature of an object for
detection is 80.degree. C.
Referring to FIG. 18, the sensor output Vout is shown as being greatest
when the ration Lb/La is 0.82. FIG. 18 does not show the other data when
the temperature of an object for detection is not 80.degree. C., but the
sensor output Vout is shown as being greatest when the ratio Lb/La is 0.82
as the same as the analysis.
FIG. 18 also shows output errors. The errors correspond to the percentage
difference between the respective value of the sensor output Vout and the
largest value thereof if the largest value of the sensor output Vout is
standardized to 100%.
In the present embodiment, the infrared ray absorbent layer 10 is formed by
screen printing. As mentioned above, the screen printing can be performed
at low cost, but size errors and shape errors of the infrared ray
absorbent layer 10 may be typically .+-.10% of the value of Lb if the
infrared ray absorbent layer 10 is formed by screen printing. Accordingly,
such an error range when the ratio Lb/La is 0.82 and the sensor output
Vout is greatest, the sensor output Vout produces acceptable outputs when
the ratio Lb/La is 0.75 to 0.90.
Further, it is preferable that the output error is at most .+-.3% of Lb in
view of typical data processing circuit requirements. As shown in FIG. 18,
a range where the ratio Lb/La is 0.75 to 0.90 satisfies the requested
output error range. Therefore, in the present embodiment, the ratio Lb/La
is set in a range of between 0.75 to 0.90.
According to the present embodiment, it is possible to increase the sensor
output Vout by setting the ratio 0.75 to 0.90 without lengthening the
sensor tip (i.e., the substrate 1) size.
Modification
In the first to third embodiments, carbon paste is used for forming the
infrared ray absorbent layer 10. However, other materials can be
alternatively used for forming the infrared ray absorbent layer 10.
Contact type screen printing can be alternatively employed for forming the
infrared ray absorbent layer 10. In this case, the pressure F3 that is
equal to the squeezer pressure F1 should be at most 0.25 MPa in order not
to damage the membrane because the restitution force F2 is zero (FIG. 7).
As shown in FIG. 4, the side of the first surface 1a of the substrate 1 is
covered with the protection layer 30 during the etching process for
forming the opening portion 2. However, the protection layer 30 is not
needed if the etching can be performed from only a side of the second
surface 1b of the substrate 1. In this case, it is possible to reduce
manufacturing cost of the infrared ray sensor because a forming process of
the protection layer 30 and a removing process thereof are not needed.
In the third embodiment, sizes, shapes, materials or the like of the
substrate 1, the membrane, the thermoelectric couples 11, 12, infrared ray
absorbent layer 10 or the like can be alternatively changed.
While the above description is of the preferred embodiments of the present
invention, it should be appreciated that the invention may be modified,
altered, or varied without deviating from the scope and fair meaning of
the following claims.
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