JPS6217177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pyroelectric linear array infrared detecting element in which a large number of pyroelectric infrared detecting elements are arranged in a line, and a method for manufacturing the same.

A pyroelectric photodetector is a thermal photodetector with the characteristics that its sensitivity is less dependent on light wavelength, and that it has a relatively fast response speed and high sensitivity for an infrared detector that operates at room temperature. A pyroelectric linear array infrared detecting element has been devised in which a plurality of element groups are arranged in a linear array, as well as when used as a single element.

In the case of a linear array infrared detection element, it is desirable to make the arrangement as fine as possible in order to improve the spatial resolution in relation to the optical system.

However, when a fine array is used, crosstalk between adjacent elements mainly due to thermal diffusion becomes a problem.

Conventional linear array elements include those in which minute elements 11 are arranged one by one on a support plate 12, as shown in Figures 1a and b, and long and narrow pyroelectric elements as shown in Figures 2a and b. As shown in FIG. 3, a single plate 21 is used as it is, with a ground electrode 23 formed on one surface and only signal extraction electrodes 22 arranged in a linear array on the other surface. A single plate 21 separated into a linear array with a part of its thickness left, or electrodes 4 on both sides as shown in FIGS. 4a and 4b.
The pyroelectric single plate 41 formed with 2 and 43 is attached to the support plate 44.
It is common that the post-focal electrodes 41 are fixed and completely separated mechanically into a linear array.

The separation type element shown in Figure 1 is difficult to finely arrange due to element manufacturing, and the normally required fineness is 0.1 mm.
It is possible to arrange about 100 elements at a certain pitch.
Very difficult.

On the other hand, a single plate structure as shown in FIG. 2 allows a fine array to be formed relatively easily, but since the pyroelectric material is a single plate, crosstalk between adjacent elements is large. This crosstalk is mostly caused by thermal diffusion within the pyroelectric element plate 21.

Therefore, as shown in FIG. 3, in order to separate the elements, a configuration has been devised in which the pyroelectric element plate 21 is separated leaving a part in the thickness direction. are not separated, so crosstalk cannot be fundamentally eliminated. Therefore,
As shown in Fig. 4, an attempt has been made to completely separate the pyroelectric element plate 41 by supporting it with a support plate 44 with low thermal conductivity, but this does not prevent crosstalk due to heat diffusion through the support plate 44. .

The present invention has been made to eliminate these drawbacks, and aims to reduce crosstalk caused by thermal diffusion and improve sensitivity. The present invention is a pyroelectric type in which the photosensitive parts of each element are spatially separated, and with the aim of improving sensitivity and further improving thermal insulation, the photosensitive parts are suspended in the air, making fine arrangement relatively easy. A linear array element and a method for manufacturing the same are provided. The present invention will be explained in detail below based on Examples.

Embodiment 1 FIG. 5 shows the structure of a pyroelectric linear array infrared detection element in an embodiment of the present invention. A window 56 is punched out in the center of the support substrate 54 so that the pyroelectric element photosensitive section 57 is suspended in the air, and the pyroelectric material 5
1, only the central photosensitive area is separated.

The output signal electrodes 52 are separated for each element, and the ground electrodes 53 of each element are connected around the central portion 50 of the support substrate 54 to be common.

The part of the output signal electrode 52 facing the window 56 becomes a photosensitive part, and the part not facing the window 56 becomes a lead wire connection part, which is usually vapor-deposited with aluminum.
Fine gold wires or fine aluminum wires are connected by ultrasonic bonding or other methods and connected to a driving circuit system so that the signals can be read out in a time-sequential manner.

The end of the pyroelectric element 51 is adhesively fixed to the support plate 54 with a conductive adhesive 55, and the photosensitive section 57 is held in a suspended state.

When the photosensitive area is separated and suspended in this way, the photosensitive area according to the present invention is different from the separated type shown in FIGS. 1 and 4 or the notched single plate type with a support plate. Since the element has no contact with the support plate, the temperature rise of the element due to infrared input is large enough to minimize the diffusion of heat, resulting in high sensitivity. In this case, heat conduction from the photosensitive area in the direction perpendicular to the linear array direction is If consideration is given to making the distance to the support end larger than the element thickness and pitch width, the effect will be even greater. Furthermore, since the diffusion of heat by radiation is usually negligible compared to the diffusion by conduction, the effect of no heat diffusion to the support plate is significant.

FIG. 6 is an operational circuit diagram of a combination of the pyroelectric linear array infrared detection element 61 and the drive section 60 as shown in FIG. 62 is a shift register, each output stage of which is connected to the gate electrode of a switch FET 63. A drain electrode of the FET 63 is connected to each element of the pyroelectric linear array infrared detection element 61.
Source electrodes of the FETs 63 are commonly connected and connected to a video signal output line 66. The output from the pyroelectric linear array infrared detection element 61 is transferred to a switch FET 63 which is successively opened by a shift register 62.
The video signal is taken out from the video signal output line 66.

In the drive circuit shown in FIG. 6, the signal readout speed must correspond to the modulation frequency of the infrared rays irradiated to the pyroelectric element 61. This modulation frequency is one parameter that determines the above-mentioned infrared detection sensitivity.

FIG. 7 shows the frequency characteristics of the voltage sensitivity of the pyroelectric linear array infrared detection element. In the figure, curve A is the characteristic of a separate type element according to the present invention in which the photosensitive part is suspended in space, and curve B is the characteristic of a conventional separate type element in which a pyroelectric element is bonded to a support plate as shown in FIG. Further, the vertical axis shows the voltage sensitivity R _V (V/W), and the horizontal axis shows the infrared modulation frequency (Hz) in logarithms.

As can be seen from Figure 7, ₁ (=1/2πτ
₁ ) If the input infrared rays are modulated at a lower frequency,
The voltage sensitivity R _V of element A suspended in the air is superior to element B attached to a support plate. In other words, the lower the infrared modulation frequency, the lower the voltage sensitivity R _V of the suspended element A.
is larger. This is because there is little heat diffusion between each element.

τ ₁ and τ ₂ in FIG. 7 are the thermal time constant τ ₁ of the element B with the support plate and the thermal time constant τ ₂ of the suspended element A, respectively, and τ ₁ <τ ₂ . This is based on the fact that the element A with less thermal diffusion takes longer to reach a thermal state, that is, has a larger thermal time constant.

Note that if the material, element area, thickness, and element spacing of the pyroelectric elements are the same, the noise will be almost the same, so the infrared detection ability of the suspended element can be evaluated by the voltage sensitivity ratio. Become.

Regarding crosstalk, it is clearly improved when compared to the single-plate type shown in Figure 2, and when the pitch is 100 μm and the element spacing is 20 μm, the crosstalk is 1/10 to several tens of minutes of the single-plate type. It has been reduced to 1.

Also, compared to the elements shown in FIGS. 1, 3, and 4, the supporting plates 12, 44 or the remaining pyroelectric layer 21
The element structure of the present invention is superior to the extent that crosstalk is eliminated.

Next, a method for manufacturing the pyroelectric element linear array according to the present invention shown in FIG. 5 will be explained in order of steps.

A pyroelectric element plate 51 that has been polarized in advance is wrapped thinly, and a signal electrode 52 and a ground electrode 5 are placed on both sides.
3 is deposited. The signal electrode 52 is usually made of nichrome vapor deposited, nickel vapor deposited, etc. with a sheet resistance of several hundred ohms/
Care must be taken to ensure that the infrared absorption rate is increased by depositing the film to a thickness that allows for smooth coating. The electrode material may be carbon paint, metal black electrode, etc. In short, it only needs to have good infrared absorption and conductivity for signal extraction. The lead wire extraction portion of the signal electrode 52 is usually separately deposited with aluminum so that a fine gold wire or aluminum wire can be connected by ultrasonic bonding, but this is not always necessary. For example, when using conductive adhesive, the lead wire take-out part should be
The same electrode as the light receiving part may be used. This signal electrode 52
In this case, at least the lead wire extraction portions must be separated by a distance greater than the element spacing. As shown in Figure 5, using both ends of each element, every other element is
If the lead wire take-out portions are provided so that they each extend to one end, the gap between them can be made sufficiently large.

The ground electrode 53 is formed by depositing aluminum or nichrome on the entire back surface of the pyroelectric element plate 51.

This is fixed with a conductive adhesive 55 to a support plate 54 in which a window 56 has been previously punched out in the center.

The ground can be taken out from the ground electrode 53 via this conductive adhesive 55, or printed wiring can be placed on a part of the support plate 54 in advance so that it comes into contact with the ground electrode 53 of the pyroelectric element 51. It can also be taken from its printed wiring.

Next, the photosensitive portion of the pyroelectric element plate 51 must be cut and separated in accordance with the pitch of the signal electrode 52.

For example, there is a method of making cuts using a YAG or carbon dioxide laser processing machine. In this case, it is important to blow away the removed pyroelectric material with an air blower during processing to prevent it from re-attaching. Further, the cut separation is adjusted so that the ground electrodes 53 are commonly connected around the hollow portion 50 of the support plate 54.

Other methods include chemical etching;
Alternatively, there is also a method using a finely moving disc cutter.

Note that this processing procedure may be performed before being fixed to the support plate 54. In this way, the photosensitive portion-separated linear array pyroelectric element shown in FIG. 5 can be manufactured.

Embodiment 2 In the above processing method, the fixed end of the signal lead wire extraction portion may not be cut all the way to the ground side, but a shallow cut may be made for the purpose of separating the signal electrodes.

In this case, since the central photosensitive area and the depth of the cut are different and a step must be created, the power of the YAG laser or carbon dioxide laser processing machine is adjusted to achieve the above purpose. Furthermore, when using a chemical etching method, this purpose can be achieved by etching in two parts.

Embodiment 3 In the above processing method, as shown in FIG. 8, the support plate 84 was not particularly hollow punched, but the pyroelectric element 81 was thinned so that a recess was formed on the ground side of the photosensitive section 87. It is also possible to use a method in which electrodes are deposited on both sides and the entire surface, and then cut in a linear row to separate the electrodes.

In this case, the ground side of the pyroelectric element 81 is first etched into a concave shape using a chemical etching method or an ion milling method, and then the central photosensitive portion 87 is removed.
Cut it into an extremely thin plate.

In this state, electrodes 82 and 83 are attached to both surfaces and fixed to a support plate 84 with a conductive adhesive 85, and the pyroelectric element photosensitive portion 87 is cut and separated. In this case, the electrodes 83 are commonly connected around the central photosensitive section 87,
It is configured so that it can be taken out as a ground from the support plate 84 portion continuously with the conductive adhesive 85. Since the periphery of the pyroelectric element is in the form of a thick plate, even if the central photosensitive portion 87 is completely separated and suspended in the air, it can be supported by this periphery.

Furthermore, the thickness of the pyroelectric element must be made considerably thinner in order to improve its sensitivity. For example 30~10μm
However, it is quite difficult to attach such a thin element to the holding plate. In this respect, in the case of Example 3, since the peripheral part of the pyroelectric element is thick,
Although advantageous, it still requires considerable care in handling.

Therefore, a method can be considered in which an electrode is attached to the ground surface of a somewhat thick pyroelectric element, that surface is adhered to a holding plate, and the pyroelectric element is wrapped into a thin plate while being adhered to the holding plate. According to this method, there is no need to handle the thin plates individually, making the work extremely easy.

FIG. 9 shows the structure of the element in this case. The support plate 94 has a central portion 90 punched out, but this is due to the process order in which the pyroelectric element 91 is made thin and then only the portion corresponding to the central photosensitive area is removed using an etching method or the like. do. Also, earth electrode 9
3, it is possible to use a separation processing method as in Embodiment 1 or 2, but if a structure is adopted in which the pyroelectric element is completely separated as shown in FIG. 9, the support plate 94 Ground the terminal using metal, semiconductor, or other conductive material.

It is better to process the support plate 94 so that the central portion 90 is cut into a concave shape in advance.
This is advantageous when the central part is to be completely removed later.

The processing procedure is as follows.

(1) The element 91 is thick (approximately 150μ or more) and the electrode 93 is attached to the entire surface only on the ground side.

(2) The support plate 94 is thinned by scraping off the portion that will later contact the photosensitive portion of the pyroelectric element from the opposite side.
This may be by chemical etching or, if metal, by machining.

(3) Fix the element ground side and the flat side of the support plate 94 with conductive adhesive 95.

(4) Wrapping the pyroelectric element 91 to make it a thin plate.

(5) Remove the part that is in contact with the photosensitive area of the pyroelectric element by etching the support plate.

(6) A signal electrode 92 is deposited on the entire surface of the pyroelectric element 91.

(7) Separate and cut the pyroelectric element 91.

Note that the above steps may be performed in the order of 1→2→3→4→6→7→5, but it is necessary to take measures such as applying a protective film to prevent damage to the signal side electrode during etching in step 5.

As described above, the pyroelectric linear array infrared detection element of the present invention is characterized in that the photosensitive parts are suspended in the air, completely separated from each other, and supported and connected only at the ends of each element, Because of its structure, it has high sensitivity, low crosstalk, and excellent characteristics. In addition, this method of manufacturing the device utilizes a single plate, which can be separated by a relatively easy processing method, and the photosensitive portion can be suspended in the air, making it easy to realize mass production.

[Brief explanation of the drawing]

1 and 2 a are plan views showing the structure of a conventional pyroelectric linear array infrared detection element, FIG. 2 b is a sectional view, FIG. 3 is a sectional view, and FIG. 4 a is a plan view, FIG. 5b is a sectional view of the same, FIG.
The figure is an operational circuit diagram of a combination of the pyroelectric linear array infrared detecting element and the drive unit according to the present invention, FIG. 7 is a diagram showing the frequency characteristics of voltage sensitivity of the pyroelectric linear array infrared detecting element, and FIG. 9A is a sectional view showing the structure of another embodiment of the linear array element according to the present invention. FIG. 9A is a plan view of the other embodiment, and FIG. 11, 21, 41, 51, 81, 91...Pyroelectric element, 12, 44, 54, 84, 94...Support plate, 22, 42, 52, 82, 92...Signal electrode, 23, 43, 53 , 83, 93... Earth electrode, 55, 85, 95... Conductive adhesive, 60...
...Drive unit, 61...Pyroelectric linear array infrared detection element, 62...Shift register, 63...
FET.

Claims (1)

[Scope of Claims] 1. A group of pyroelectric infrared detection elements arranged in a straight line with the photosensitive parts of each element separated spatially and thin film electrodes formed on both sides, and a support substrate with a hollow center. pyroelectric linear array infrared detection, characterized in that both ends of the pyroelectric infrared detection element are fixed to the support substrate so that the photosensitive part of the pyroelectric infrared detection element is suspended in the air. element. 2. The pyroelectric linear array infrared detection element according to claim 1, wherein one of the thin film electrodes is commonly connected on a support substrate. 3. A pyroelectric linear array according to claim 1, wherein a group of infrared detecting elements is formed linearly in a thin part of a photosensitive element plate having a thick center part, and this element group is separated from a support substrate. Infrared detection element. 4. The pyroelectric linear array according to claim 1, wherein the support substrate is made of a conductive material or a semiconductor, and the pyroelectric element is fixed in contact with the support substrate in an electrically conductive state. Infrared detection element. 5 Step of forming a signal extraction electrode on one side of the pyroelectric element plate and a ground electrode on the other side, a step of fixing the pyroelectric element plate on a support substrate, and a step of microfocusing the photosensitive part of the pyroelectric element plate. A pyroelectric linear array infrared detection element comprising at least the steps of separating the electronic elements into a linear array arrangement, and making the photosensitive portion of the pyroelectric element plate and the support substrate non-contact. Production method. 6 Signal extraction electrodes are arranged and deposited in a linear array on a pyroelectric element plate that has been thinned in advance, and a ground electrode is deposited on the entire surface facing the plate, and then this pyroelectric element plate is processed to be hollow in the center in advance. The pyroelectric linear array infrared detecting element according to claim 5, wherein the pyroelectric linear array infrared detecting element is fixed to a support substrate which has been provided with a pyroelectric element plate, and then only the photosensitive part of the pyroelectric element plate is separated in accordance with the pattern of the signal extraction electrode. Production method. 7. A signal extraction electrode and a ground electrode are vapor-deposited on both surfaces of the pyroelectric element plate, which has been thinned in advance, and fixed to a support substrate whose central part has been made hollow, and then the photosensitive part of the pyroelectric element plate is attached. manufacturing a pyroelectric linear array infrared detecting element according to claim 5, wherein the fixing part is processed to separate only the signal electrodes into a linear array without separating the ground electrode. Method. 8 In advance, only the photosensitive part of the pyroelectric element plate is thinned, and at least the photosensitive part on the ground electrode side is processed to be recessed from the peripheral fixing part, and the signal electrode and the ground electrode are deposited on the entire surface of both sides, and this is supported. The pyroelectric linear array infrared detecting element according to claim 5, which is fixed to a substrate and then processed so that the photosensitive parts are completely separated in the form of a linear array, and the peripheral fixed parts remain partially unseparated. manufacturing method. 9. A pyroelectric element plate, on which a ground electrode is completely vapor-deposited on one side, is fixed on the flat side of the support plate, which has been processed in advance so that one side of the central part in contact with the pyroelectric element photosensitive area is recessed, on the ground electrode side. In addition, electrical continuity is established with the support plate at the peripheral portion, and then the pyroelectric element plate is made thin, a signal electrode is deposited on the pyroelectric element plate, and the pyroelectric elements are separated into a linear array. 6. The method of manufacturing a pyroelectric linear array infrared detecting element according to claim 5, further comprising a step of removing the thin support plate left at the center of the support plate by etching.