Note: Descriptions are shown in the official language in which they were submitted.
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PYROELECTRIC DETECTOR AN~ METHOD
FOR MANUP'~CTURING T~E SAME
BACKGROUND OF THE INVENTION
This invention relates to a device for detecting infra-
red rays utilizing the pyro~lectric effect and methods for
manufacturing the same.
Generally, pyroelectric materials are use in pyroelec-
tric detectors for detecting infrared rays by utilizing the
pyroelectric effect. However, if the heat capacity of the
pyroelectric material is great, the pyroelectric material can-
not respond to a fast change in the energy of infrared rays.
10 Therefore, various techniques are used in the prior art to
reduce the heat capacity of pyroelectric materials. For
example, by reducing the thickness of the pyroelectric material
to about 30-50 ,um, heat capacity is reduced.
Since it now will be necessary to refer to the drawings
15 appended hereto, they will first be described briefly.
BRIEF DESCRIPTION OF THE DRAWINGS
The exact nature of this invention, as well as other objects
and advantages thereof, will be readily apparent from conside-
ration of the following specification and drawings.
Figure 1 shows a longitudinal sectional view of one
prior art embodiment of a pyroelectric detector.
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Figure 2 shows a longitudinal sectional view of
another prior art embodimen-t of a pyroelectric detector.
Figure 3 shows a longitudinal sectional view of a
third prior art embodiment of a pyroelectric detector.
Figure 4A shows a longitudinal sectional view of one
embodiment of the pyroelectric detector of the present
invention.
Figure 4B shows a perspective view, partly in
section, of the pyroelec-tric detector shown in Fiyure 4~.
Figure 5 shows a wiring diagram Eor the pyroelectric
detector.
Figure 6 illustrates a sequence of steps in accor-
dance with one method of making the pyroelectric detector.
Figure 7 illustrates a sequence of steps in accor-
dance with another method of making the invention.
Figure 8 illustrates a sequence of steps in accor-
dance with a further embodiment of the method of the invention.
In the prior art, heat capacity also is reduced by
exposing the pyroelectric material to air and mounting the
pyroelectric material on a heat insulated substrate. A
technique for exposing the pyroelectri~ material to air is
shown in Fig. 1. A piezoelectric crystal 3 is mounted on a
stand 5 by the wires 4 and 5. The electrode 1 for receiving
infrared rays and the shield electrode 2 are formed on
different sides of the piezoelectric crystal 3. Although
heat capacity is reduced, the pyroelectric detector shown
in Figure 1 is not reliable or durable; it also is very
difficult to manufacture and treat the pyroelectric
detector because the pyroelectric crystal 3 is so thin.
Another prior art technique is shown in Figure 2.
The shield electrode 2, which is formed on one side of
piezoelectric crystal 3, is connected to the heat insula- ~
ted substrate 6 which is in turn mounted on the stand 5.
The pyroelectric detector shown in Fig. 2 has the dis-
advatantage that it is difficult to connect wire 4 to the
shield electrode 2.
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Another known structure is shown in Fig. 3. This
structure is described in Japanese patent publication No.
12272/1976 ~Tokkosho~. The shield electrode 2, which is
mounted on one side of piezoelect:ric crystal 3, is formed
around a heat insulated substrate 6 and mounted on stand
5 by conductive glue. The heat insulated substrate 6 is
covered by an SnO~ film 7 so it is unnecessary to connect
the shield electrode 2 to stand 5 by wire 4. However,
because the piezoelectric crystal 3 is mounted on the sub-
strate 6, the heat capaci-ty is great which prevents the
detector from responding to fast changes in the energy of
infrared rays. It also is difficult to manufacture and
treat the detector shown in Figure 3 because it is neces-
sary to mount a very thin pyroelectric crystal.
SUMMARY OF THE INVENTION
.
It is an object of an aspect of this invention to
provide a pyroelectric detector which can respond to fast
changes in the energy of infrared rays. It is an object
of an aspect of this invention to provide a pyroelectric
detector:having a strong structure, high durability and
high reliability.
It is an ob]ect of an aspect of this invention to
provide an improved method for manufacturing pyroelectric
detectors using thin pyroelectric material. An object of
an aspect of this invention is to provide a method which
can be readily used for mass production of pyroelectric
detectors.
According to an aspect of this invention, certain
of these objects are attained by providing an improved
pyroelectric detector. This pyroelectric detector com
prises a pyroelectric material, an infrared receiving
electrode mounted on one face of the pyroelectric
material for receiving infrared rays, a shield electrode
mounted on the other face of the pyroelectric material, a
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a substrate made of a semiconductive or concluctive ma-terial
having a hole hroader than the inErared receiv:ing elec-trode,
the substrate being connected to the shield electrode by
conductive glue, and a stand to which the substrate is con-
nected by conductive glue.
Also, according to an aspect of this invention,
certain of these objects are attained by providing various
methods of manufacturing pyroelectric detec-toxs. A shield
electrode is formed on one face oE a wafer of pyroelectric
material and holes are made in a substrate of semiconduc-
tive or conductive material which is glued to the shield
electrode by conductive glue. The other face of the wafer
of pyroelectric material is ground and infrared receiving
electrodes are formed thereon for receiving infrared rays
Each infrared receiving electxode, which has an area sub-
stantially less than the area of each hole in the substrate,
is positioned over one of the holes. The wafer of pyro-
electric material than is diced at positions between the holes.
Various apsects of the invention are as follows:
A pyroelectric detector comprising:
a pyroelectric materiali
an infrared receiving electrode mounted on one face of
said pyroelectric material for receiving infrared rays;
a shield electrode placed at the other face of said
pyroelectric material;
a substrate made of semiconductive or conductive
material fastened to said shield electrode by conductive glue,
said substrate having an enclosed aperture substantially broad-
er than said infrared receiving electrode; and
a stand to which said substrate is fastened by conduc-
tive glue.
A method of manufacturing pyroelectric detectors com-
prising the steps of:
forming a shield elec-trode on one face of a wafer of
pyroelectric mat:erial;
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fastening a substrate made of semiconductive material
to said shleld electrode by conductive glue;
grinding the other face of said wafer of pyroelectric
material;
makiny enclosed apertures in said substrate;
forming infrared receiving electrodes for receiving
infrared rays on the other face of said wafer of pyroelectric
material, each of said receiving electrodes having an area
substantially less than the area of a corresponding one of
said enclosed apertures, each of said infrared receiving
elec~rodes being positioned over one of said enclosed aper-
tures on said other face of said shield electrode; and
dicing said pyroelectric material at positions
between said enclosed apertures.
A method of manufacturing pyroelectric detectors
comprising the steps of:
forming a shield electrode on one face of a wafer
of pyroelectric material;
making enclosed apertures through a substrate made
of semiconductor or conductive material;
fastening said substrate to said shield electrode
by conductive glue;
grinding the other face of said wafer of pyro-
electric material;
forming infrared receiving electrodes for receiving
infrared rays on the other face of said wafer of pyroelec-
tric material, each of said infrared receiving electrodes
having an area substantially less than the area of each of
said enclosed apertures, each of said infrarad receiving
electrodes being positioned over one of said enclosed
apertures on said other face; and
dicing said pyroelectric material at positions
between said enclosed apertures.
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A method of manufacturing pyroelectric detectors
comprising the steps of:
forming a shield electrode on one face of a wafer of
pyroelectric material;
forming a conductive thick-film paste on said shield
electrode, said thick-film paste having enclosed apertures
therein;
grinding the other face oi- said wafer of pyroelec-
tric material;
forming infrared receiving electrodes for receiving
infrared rays on the other face of each pyroelectric material,
each of said i.nfrared receiving electrodes having an area
substantially less than the area of each said enclosed
apertures, each of said infrared receiving electrodes being
positioned over one of said enclosed apertures on said
other face; and
dicing said pyroelectric material at positions
between the enclosed apertures.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 4A shows a cross-sectional view of the prefer-
red embodiment of the pyroelectric detector of the invention.
The crystal
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Il is n waîcr of pyroelectric material, such as a wroelectric crystal
lilce LiTaO3. The pyroelectric cryst~l 11 is flpproximately 50 ~Jm thiclc
and measures 3.5mm by 3.5mm.
An infrared receiving electrode 12, which receives infrured rays,
is mounted on tlle upper face of pyroelectric crys~al 11. The infrared
receiving electrode 12 is a ~3isk ~vhic}l measures 2mm in diameter, At
the other face o~ wroelectric crystal 11 is a shield electrode 13; shield
electrode 13 covers. the whole face of crystal 1]. A substrate 15 ma~le
of semiconductive material sucll ns silicon is fastened to the shield
~lectrode 13 by conductive glue 14. The main plane, of silicon substrate
15 has an orientation in the (100) plane; it measures 250 ,um tilick nnd
is a square measuring 3.5 mm by 3.5mm. In the center of silicon
substrate 15 is a square hole 16 which measures 2.5mm by 2.5mrn. The
hole 16 is made by selective etching. The position of the open nrea
of hole 16 corresponds to the position of infrared receiving electrode 12
although hole 16 is substantially broader than infrared receiving electrode
12. The legs of silicon substrate 15 nre fastened to stand 18 by conductive
glue 17. The stand 18 and the lead terminal 20 are insulated frorn each
otller by insulating material 19. A lead wire 21 electrically connec.s
lead terminal 20 and the ;nfrared receiving electrode 12. Lead wire 21
-;s made of a material such as gold or aluminum.
The pyroelectric detector shown in Figure 41~ is mounted and
~ssembled in a package as shown in Figure 41B and an electric circuit
for the pyroelectric detector of Figure 4B is shown in Pigure 5. Jn
this embodiment~ ;nfrared receiving electrode 12 contacts conductive
supporting members 22a and 22b. On the stand next to pyroelectric
crystal 11, resistors 23 and 24 and field effect transistor FET 25 are
mounted, Stand 18 is hermetically sealed witll N2 gas by cap 2G; cap
25 has a silicon window 27 at the center. Three pillS or terminals Tl,
T2, and T3 project through stand 18. Tlle pin Tl, wl-ich is grounded,
is connected directly to stand 18; the pin T2 is connected to resistor
24 ~d the source of FET 25; and the pin T3 is connected to the drain
of FET 25. Conductive supporting member 22b is connccted to t11e
gate of FET 25 and conductive supporting member 22n is connected to
resistor 23. ~csistors 21 ~nd 24, which also ar~ colmected to S;~
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18"1~ve resistallce values of 1011 and 10~ ollms, respectivcly. Whcn
infrared rays pass through silicon window 27, they strikc infrared recci~ing
electrode 12 producing an output voltnge between pin Tl and pin T2.
In the embodiment shown in Figures ~A and 4B, the ~eat
capacity is small because of the hole in substrate 15. Also, it is
Imnecessary to interconnect shield electrode 13 and stand 18 with wire
because substrate 15 is made of conductive or semiconductive material
sucll as silicon and the suhstrate is fastened by conductive glue 1~ and
17. l~urthermore, this pyroelectric detector is durable because pyroelectric
cr~7stal 11 is supported by substrate 15.
The pyroelectric detector sllown in E~igure 4A is manufactured
in accordance with the method shown in Pig. 6. In ~ig. 6(a), a sllield
ëlectrode 13 is formed on a pyroelectric crystal wafer 31 which rneEIsures
63mm in diameter and 250 ,um thick and wl~ich is made of a Z suhstrate
of LiTaO3. The shield electrode 13, which may be made of nichron e,
is formed by vacuum evaporation or sputtering. In Figure G(b), nn oxide
film is formed on one face of a silicon substrate 15 wilich measures
63mm in diameter and 2S0 ~um thick. The silicone substrate has an
orientation (100). The oxide film 32 has square holes measuring 2.8mm
x 2.8mm and it acts as a mask pattern for etcll;ng. P~s shown in ~ re
6(c), the other face of silicon substrate lS is fastened to the shield
electrode 13 of the wafer 31 by conductive glue 1~. Then, as shown in
Fig. 6(d), the other face of the pyroelectric crystal wafer 31 is ground
until the ~vafer achieves a thickness of 5û JUm~
The combined pyroelectric crystal wafer 31 and silicon substrate
15 is dipped into liquid Hydrazine at 100 C. The Hydrazine has a fast
etching rate in tlle (100) direction and a slow etching~ rate in the ~111)
direction. Therefore, silicon substrate 15 is etclled selectively at a 57
angle against the (100) face of tlle crystal. By selective etchiJlg, square
holes 16, which each measure 2.5mm x 2.5mm, are made in silicc)n
. substrate 15 as shown in ~ig. 6(e). As shown in ~igO 6(f), the oxide
film 32 is removed and infrared receiving electrodes 12 are formed on
tlle ground face of wafer 31. Each electrode 12 is a disk measul ing
2.0n~n in diameter. The position of each electrode 12 corresponds to
tlle position of a hole 16 and eacll electrode 12 ilas an area substnlltially
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less than the area of the corrcsponding hole 16.
~ igure 6(g) is an upper vie~v of the wafer 31 after completior
of the steps in Fi~lres 6(n~(f). In Figure 6(g), the dotted line s~uares
indicate holes 16 altl10ugll the nctual distance between holes IG is grcater
than shown in Figure 6(g). The wafer 31 is diced between holes lG by
a dicing machine to form n plurality of chips as shown in ~igures 6(h)
nnd 6(i). The cllip then is mounted on stand lS alld fastened by
conductiYe glue 17 as shown in ~igure 6(j).
The method shown in Fig. 6 makes it easy to manufllcture
pyroelectric detectors because one large wafer is used. Ther~fore, it
is possible to mass-produce the pyroelectric detectors. Also7 by using
a universal dicing machine, cheap pyroeleotric detectors can be obtailled.
Yarious modificat;ons can be made in the method sho-Nn in
~igure 6. Instead of the silicon substrate 15g substrates made of Ge,
~aAs, or Gap can be used. Also, the step of making holes may be
done before the step of grinding the other fnce of pyroelectric crys.al
wafer 31.
~ igure 7 shows another embodiment of the invention for
~nanufacturing pyroelectric detectors. A shield electrode 42 is formcd
on one whole side of pyroelectric crystal wafer 41 in ~igure 7(a)~ As
shown in lFig. 7(b), circular holes 43 are made through a substrate 44.
The substrate ~4 is made of a semiconductive or conductive material
such as Si, Ge, GaAs, GaP, or metal. Circular holes 43 are mnde by
a-conventional mechanical process such as an ultrasonic horn method or
a sand brass method.
As shown in Pigure 7(c), substrate 44 is fastened to the shield
electrode 42 OI the wafer 41 by conductive glue 15. In ~igure 7(d),
tlle other face of the pyroelectric crystal wafer 41 is ground until the
wafer is ~bou~ 50 ~m thick. In Figure 7(e3, on the groulld face of
wafer 41, infrared receiving electrodes ~6 are formed. Each of the
infrared receiving electrodes 46 is a disk, and the diameter of each
disk is less than the diameter of each circular hole 43. The pOSitiOll
of each infrared receiving electrode 46 corresponds to the position a
hole ~3. Then, as shown in ~igures 7(f) and ~g~, bonding electrodcs A7
are formed between infrared recciving electrodes 46. ~ re 7(~) sIIolls
-- 7 ~
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~n upper view of the w~ifer ~1 in which IIOIGS ~3 are dcsignated by
dotted lines.
The wafer ~1 shown in Figure 7(g) is diced into chips by a
~miversal dicing machine between circular holcs 43. ~igurcs 7(il) and
~(i) show an individual chip. The chip of pyroelectric crystal 48 is
mounted on stand ~9 by conductive glue 50 as shown in ~igure 7(j). ~;
lead terminal 51, whicll is supported by insulating malerial 52, is
~leetrically connects~d ~o bonding electrode 47 by lead wire 53. Bonding
electrode 47 corresponds to conduc:tive supporting members 22a and 22b
in Figure ~B. l'he pyroelectric detector in Figure 7(i) is assembled ns
shown in Figure 4B.
In the method shown in ~igure 7, the step of rnnlcin~ holes is
done by a meehanical proeess7 and the time to manufactue pyroelectric
detectors. is short. The pyroeleetrie detector manufactured aceordirlg
to Figure 7 is more durable than the pyroelectri e deteetor of ~igure 6
because the hole 46 OI substrate 44 is cireu'lar and the contact area
between substrate 44 and stand 49 is large.
Figure 8 shows yet another embodiment of the invention for
nanufacturing pyroelectric deteetors. A shield eleetrode G2 is formed
on one whole side of pyroelectric erystal wafer Gl in Figure 8(a). Ne~ct,
as shown in Figure 8(b), a substrate 63 made of conduetive thick--film
paste and having cireular holes 64 is formed on tlle shield electrode
62. The conduetive thick-film paste is applied to the shield eleetrode
62, except in areas where the holes 64, are made, by' screen printing
for one hour. The s~onductive thiclc-film paste then is balced for one
hour.
~ s shown in ~igure 8(c), the other face of wroelectrie erystal
wafer 61 is ground until the thiclcness is about 50 mm. As sho~vn in
Figure 8(d), on the ground faee of wafer 61~ infrared receiving electrocies
¢5 ~re formed. l'he infrared reeeiving eleetrodes 65 nre Iormed by
sputtering or vaecum evapor~tion of nichrome. Each of the infrared
reeeiving electrodes 65 is a disk whieh measures 2.0 mrn in diameter;
the diameter of eleetrodes G5 is less than the diameter OI each of the
eireular holes 64. The position of each electrodc G5 corresponds to tllc
position of a hole 64. Bonding electrodes 6û are îormed adjaccnt to
r3
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and in cont~ct with the ~nfr~lred receivillg electrodes G5 ns sl~owl-l in
I~igure 8(e~. Bonding electrodes 66, which al e m~de of aluminum ubout
l ~um thiclc, are formed by vaccum evaporllt;on.
The wafer 61 is diced between holes 64 at the dotted line
positions shown in Figure 8(e) by a universal dicing machine to form
individual chips. A ehip then is mounted on stand 68 and f~stened by
conductive glue 69. The chip 67 is ~ssembled and pack~ged ~ sJlown
in ~igure 4B.
In the method shown in Figure 8, it is e~sy to manui~nc~ure
pyroelectric detectors because a substrflte 63 made of conductive thiek-
film paste is directly formed on the wroelectrie crystal wafel ~l without
ma',~ing holes.
ln all the embodiments OI the method of this invention,
pyroeleetri,e crystals such as a crystal of I.iTaO3 are used ~s elements
for detecting infrared rays. Other pyroelectric materials can be used
such as triglycine sulphate (TGS), stroiltium barium niobate (SBN), PbTjO3
~nd PZT - type ferroelectrie ceramics.
~ lthough illustrative embodiments of the invention have been
deseribed in detail with referenee to the accompanying drawings, it is
to be understood that various changes and rmodifications could be effected
therein by are slcilled in the art without departing from the scope and
spirit of the invention.
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