JP2011158436A - Infrared detection element and infrared detector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an infrared detection element and an infrared detector which can efficiently absorb incoming infrared ray and effectively utilizing infrared energy obtained. <P>SOLUTION: A pyroelectric element layer including pyroelectric elements 10, 11, and 12, which include a pyroelectric body 2 where the value of spontaneous polarization varies with increase of temperature to create surface charge, an upper electrode 3 arranged on top surface of the pyroelectric body 2, and a lower electrode 4 arranged on bottom surface of the pyroelectric body 2 configures the infrared detection element 100 containing two or more-layered pyroelectric element layer arranged at upside and downside thereof. Moreover, the infrared detector including the infrared detection element 100 is also configured. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an infrared detection element and an infrared detection device that receive and detect infrared rays. In particular, the present invention relates to a pyroelectric infrared detecting element and an infrared detecting device that generate surface charges by a change in spontaneous polarization.

Sensors and detection elements for detecting received infrared rays are roughly classified into two types called quantum type and thermal type depending on the operating principle. In particular, a thermal-type infrared detection element that absorbs incident infrared rays and detects infrared rays by changing the temperature of the light receiving element has an advantage that cooling is unnecessary.
For this reason, in recent years, it has come to be used as an imager of an infrared imaging device (thermography), a human sensor mounted on an eco product or the like.

  For example, the following three types of thermal infrared detection elements are known. One is a thermopile type to which a thermocouple that generates the Seebeck effect is connected. The other is a bolometer type using a change in resistance value due to temperature rise. A pyroelectric type that generates surface charges by a change in spontaneous polarization of the pyroelectric element is known.

  In particular, pyroelectric infrared detectors have been studied to increase the pyroelectric coefficient, which is the efficiency of surface charge generation due to temperature changes, by devising the type and composition of pyroelectric materials in order to increase the sensitivity to infrared rays. There are many active studies to absorb infrared rays efficiently.

For example, in the following Patent Document 1, a hollow structure in which an infrared absorption part is floated on a temperature sensor by a support column is used.
This is intended to increase the area of the infrared absorbing portion as much as possible by arranging the infrared absorbing portion independently by the support pillar. That is, the aperture ratio, which is the ratio of the detectable sensor area to the area of the pixel region, is increased.

Patent Document 2 below discloses that an organic thin film made of photosensitive polyimide is formed on a pyroelectric element via a SiO ₂ layer. This is intended to increase the infrared absorption efficiency by absorbing not only the pyroelectric element but also the organic thin film.

Japanese Patent No. 3944465 Japanese Patent No. 2523895

However, in the case of the above-mentioned patent document 1, since infrared rays are detected for each pixel arranged in an array after all, the infrared absorption part must also be divided and arranged for each pixel. Accordingly, a gap is always generated between adjacent infrared absorbing portions, and the aperture ratio cannot be 1.
Furthermore, the smaller the pixel size, the greater the ratio of the gap to the area of the infrared absorbing portion, so the efficiency of infrared absorption will decrease.

  Moreover, what actually detects infrared rays is a temperature sensor connected to the infrared absorbing portion by a support column. In Patent Document 1, a diode or a transistor is used for the temperature sensor, and infrared rays are detected by changing the electrical characteristics of the diode or the transistor due to a temperature change.

Therefore, the heat obtained by the infrared absorption part absorbing infrared rays must be transmitted to the temperature sensor through the support column.
That is, not all the heat obtained by the infrared absorption is used for increasing the temperature of the temperature sensor, and the infrared absorbing portion and the support column similarly increase in temperature.
For this reason, only the heat capacity of the infrared absorption part and the support column is always lost, and all of the incident infrared energy cannot be used.

Also in Patent Document 2, it is a pyroelectric thin film that detects infrared rays. Therefore, similarly, in order to transmit the thermal energy obtained by the organic thin film to the pyroelectric thin film, a loss corresponding to the heat capacity of the organic thin film and the SiO ₂ layer is generated.

  The present invention has been made in view of the above problems. That is, an object of the present invention is to provide an infrared detection element and an infrared detection device that can efficiently absorb incident infrared rays and can effectively use the obtained infrared energy.

  The infrared detection element of the present invention has a pyroelectric material that changes its spontaneous polarization value due to an increase in temperature and generates surface charges, an upper electrode disposed on the upper surface of the pyroelectric material, and a lower surface of the pyroelectric material. A pyroelectric element layer comprising a pyroelectric element having a lower electrode disposed thereon; And the pyroelectric element layer of two or more layers arrange | positioned up and down is included.

An infrared detection device according to the present invention includes a light collecting unit that collects infrared light from an imaging target.
In addition, a pyroelectric material that changes its spontaneous polarization value due to an increase in temperature, generates a surface charge, an upper electrode disposed on the upper surface of the pyroelectric material, and a lower electrode disposed on the lower surface of the pyroelectric material. A pyroelectric element layer comprising a pyroelectric element having And the infrared detection element which receives the infrared rays condensed by the said condensing part is provided including the said pyroelectric element layer of 2 or more layers arrange | positioned up and down.
A drive circuit for driving the infrared detection element and a signal processing circuit for processing an output signal from the infrared detection element are provided.

  According to the infrared detection element of the present invention, it includes two or more pyroelectric element layers arranged one above the other. For this reason, infrared rays that could not be absorbed by a single pyroelectric element layer can be absorbed by the pyroelectric element layer disposed therebelow.

  Moreover, according to the infrared detection device of the present invention, the infrared detection element including two or more pyroelectric element layers arranged above and below is provided. For this reason, the infrared rays that have been transmitted through the upper pyroelectric element layer can be absorbed by the pyroelectric element layer disposed in the lower layer.

  According to the present invention, infrared rays that could not be absorbed by one pyroelectric element layer can be absorbed by the pyroelectric element layer disposed below the infrared ray. For this reason, it is possible to improve the infrared absorptance and to provide a highly sensitive infrared detecting element and infrared detecting device.

It is a schematic sectional drawing which shows the infrared rays detection element which concerns on 1st Embodiment. A is a cross-sectional view showing a state of polarization of the pyroelectric element in the initial state. B is a cross-sectional view showing the state of polarization of the pyroelectric element when irradiated with infrared rays. B is a cross-sectional view showing a state of polarization of the pyroelectric element. A is explanatory drawing which shows the relationship between the temperature rise which arises by infrared irradiation, and time in each site | part of the pyroelectric element of B. FIG. It is explanatory drawing which shows the relationship between the film thickness of a pyroelectric body and the amount of electric charges generated at the time of infrared irradiation. It is a schematic sectional drawing which shows the infrared rays detection element which concerns on a 1st modification. It is a schematic sectional drawing which shows the infrared detection element which concerns on 2nd Embodiment. It is a schematic sectional drawing which shows the infrared rays detection element which concerns on a 2nd modification. It is a schematic block diagram which shows the infrared rays detection apparatus which concerns on 3rd Embodiment.

Examples of the best mode for carrying out the present invention will be described below, but the present invention is not limited to the following examples. The description will be made in the following order.
1. First embodiment (example of infrared detection element)
2. First modification (example in which the pyroelectric elements are filled with an insulator)
3. Second embodiment (an example of absorbing infrared rays incident on a gap between pixels)
4). Second modified example (example in which each pyroelectric element is filled with an insulator in the second embodiment)
5. Third embodiment (example of infrared detection device)

1. First Embodiment FIG. 1 is a schematic cross-sectional view showing a configuration of an infrared detection element 100 according to a first embodiment. Here, for simplification of the drawing, the structure for one pixel is shown.
The infrared detecting element 100 according to the present embodiment includes a substrate 1 and pyroelectric elements 10, 11, and 12 that are formed on the substrate 1 and generate an electrical signal in response to an increase in temperature.

The pyroelectric element 10 has a spontaneous polarization value that changes due to a temperature rise, generates a surface charge, an upper electrode 3 disposed on the upper surface of the pyroelectric body 2, and a lower surface of the pyroelectric body 2. The lower electrode 4 is provided.
The pyroelectric body 2 is not particularly limited as long as the pyroelectric body 2 can change the value of spontaneous polarization as the temperature rises by absorbing infrared rays. For example, lead titanate and lithium tantalate are well known as inorganic materials, and glycine trisulfide (TGS), polyvinylidene difluoride and the like are well known as organic materials.

Further, it is preferable to use a conductive material that easily absorbs infrared rays for the upper electrode 3 and the lower electrode 4 to assist the temperature rise of the pyroelectric body 2. As the conductive material that easily absorbs infrared rays, for example, chromium or the like can be used.
In the pyroelectric elements 10, 11, and 12, infrared rays can be detected by taking out a change in surface charge caused by the temperature rise of the pyroelectric body 2 as a voltage signal or a current signal.

In the present embodiment, such pyroelectric elements are arranged in the vertical direction so as to form a plurality of pyroelectric element layers of at least two layers. FIG. 1 is an example in which pyroelectric elements 10, 11, and 12 are stacked one above the other to have a structure having three pyroelectric element layers (three-layer structure).
Note that spaces are formed between the pyroelectric elements or between the pyroelectric elements 10, 11, 12 and the wirings 6, 7 by, for example, sacrificial layer etching, and are insulated from each other.

  In the case of FIG. 1, for example, when the infrared ray A1 is incident on the pyroelectric element 10 arranged in the uppermost layer, the infrared ray A2 that cannot be absorbed by the pyroelectric element 10 is arranged in the lower layer of the pyroelectric element 10. Is incident on the pyroelectric element 11. The infrared rays A3 that could not be absorbed by the pyroelectric element 11 are further incident on the pyroelectric element 12 disposed below the pyroelectric element 11, and are absorbed by the pyroelectric element 12.

For example, when the infrared absorptance of each pyroelectric element is 50%, the infrared A2 transmitted through the pyroelectric element 10 has an energy amount of 50% of the infrared A1. The pyroelectric element 11 absorbs half of the incident infrared ray A2, that is, 25% of the infrared ray A1.
Then, the infrared ray A3 having an amount of 25% of the infrared ray A1 is incident on the pyroelectric element 12, and 12.5% is absorbed here.

Thus, in the case of the three-layer structure, it is possible to absorb 87.5% of infrared rays in total, and it is possible to greatly increase the absorption efficiency. Further, if the number of layers to be stacked is further increased, the absorption efficiency can be further increased.
These pyroelectric elements stacked in the vertical direction may have the same structure and configuration, or may have different structures and configurations.

Preferably, the lower electrode of the pyroelectric element disposed in the lowermost layer, for example, the lower electrode 5 of the pyroelectric element 12 in FIG. 1 is made of a material that reflects infrared rays. When the lower electrode of the lowermost pyroelectric element is made of a material that reflects infrared rays, the pyroelectric elements 10, 11, and 12 are not completely absorbed and the remaining infrared rays are reflected. Thereby, since the reflected infrared rays are again absorbed by the pyroelectric elements 10, 11, 12, the absorption efficiency can be further increased.
As such a material that reflects infrared rays, for example, Al or the like can be used.

Moreover, the wirings 6 and 7 connect the pyroelectric elements of each layer that are overlapped above and below in series. And it connects with the voltage converter, the switching circuit, etc. which are not shown in figure provided in the lower layer of the board | substrate 1 by the via etc. which were formed in the board | substrate 1, for example.
In the present embodiment, the pyroelectric elements of each layer are aligned and overlapped in the vertical direction. Therefore, for example, as shown in FIG. 1, the upper and lower pyroelectric elements 10, 11, 12 can be easily connected by the wirings 6, 7. For this reason, even if the number of pyroelectric elements is increased by adopting a multilayer structure in which the pyroelectric elements are stacked one above the other, there is no need to arrange a voltage converter or a switching circuit for each pyroelectric element, and the number of parts can be reduced. Increase can be suppressed.

  For other pixels (not shown), similarly, the pyroelectric elements of each pyroelectric element layer are aligned and overlapped in the vertical direction. In the pixels adjacent to each other, pyroelectric elements of each layer are arranged in the horizontal direction with a space therebetween.

  Thus, the infrared detection element of this embodiment has a multilayer structure in which pyroelectric elements are stacked one above the other. For this reason, since the infrared rays that could not be absorbed by one layer of pyroelectric elements can be absorbed by the pyroelectric elements arranged in a lower layer, the absorption efficiency can be increased.

Further, in the configuration described in Patent Document 2, the thermal energy absorbed in the infrared absorbing layer provided independently of the pyroelectric element is transmitted to the pyroelectric element. There was only a loss.
However, the infrared absorption layer in the present embodiment is substantially composed only of pyroelectric elements of pyroelectric elements. For this reason, the thermal energy by the absorbed infrared rays can be directly used for the polarization inversion of the pyroelectric material as it is, and the energy utilization efficiency can be further increased.
Therefore, according to the present embodiment, a more sensitive infrared detection element can be realized.

On the other hand, the infrared absorption efficiency can be increased by simply increasing the thickness of the pyroelectric material. However, simply increasing the thickness of the pyroelectric material causes problems described below.
FIG. 2 is a cross-sectional view showing a state of polarization of the pyroelectric body of the pyroelectric element. The pyroelectric element 110 here is formed on the substrate 13, and an upper electrode 15 is formed on the upper surface of the pyroelectric body 14, and a lower electrode 16 is formed on the lower surface.

  In the initial state, the pyroelectric body 14 has the same polarization direction as shown in FIG. 2A. However, as shown in FIG. 2B, when the temperature of the pyroelectric body 14 is increased by the incidence of the infrared ray A4, an electric dipole whose polarization direction is reversed appears and the balance is lost. Thereby, it will be in the state which the electric charge produced on the surface of the pyroelectric body 14, and infrared rays can be measured by detecting this.

  However, when the thickness of the pyroelectric material 14 is increased, the amount of absorption increases, but a temperature difference occurs within the same film. FIG. 3A shows a simulation of the temperature rise of the pyroelectric body 14 at each position in the film thickness direction when the pyroelectric element 110 of FIG. 3B is irradiated with infrared rays A4 from the upper electrode 15 side.

The vertical axis represents the rising temperature of the pyroelectric body 14 before infrared irradiation, and the horizontal axis represents the time from the start of infrared irradiation.
The line L1 indicates the temperature at the lower surface of the pyroelectric body 14, and the line L2 indicates the temperature at a position above the lower surface of the pyroelectric body by 1/4 of the film thickness.
Further, the line L3 is the temperature at the center of the film thickness of the pyroelectric body 14, and the line L4 is the temperature at a position below the film thickness by ¼ from the upper surface of the pyroelectric body 14.
The line L5 is the temperature on the upper surface of the pyroelectric body L14, and the line L6 is the temperature of the upper electrode 15.

When infrared rays are irradiated, the temperature rises in a short time and reaches an equilibrium state at a certain temperature. In the upper electrode 15 located on the uppermost surface, the temperature rises instantaneously and is in an equilibrium state.
As can be seen from FIG. 6, the temperature at each position is not equal even in the equilibrium state, and the temperature becomes lower toward the lower electrode 16 side. For this reason, a large amount of inversion occurs in the upper part of the pyroelectric body 14, while the inversion of polarization decreases in the lower part of the pyroelectric body 14, and unevenness in the inversion of polarization occurs in the pyroelectric body 14.
This temperature difference increases as the thickness of the pyroelectric body 14 increases, so that the polarization inversion unevenness also increases. If there is such uneven polarization inversion, infrared rays cannot be detected efficiently.

Further, when the film thickness is increased, the pyroelectric body has a larger volume, so the heat capacity is increased, and the temperature rise of the pyroelectric body is slowed down.
For example, the heat capacity H of the pyroelectric material can be expressed by the following formula (1). Where Cp is the specific heat of the pyroelectric material, ρ is the density of the pyroelectric material, A is the infrared incident area, and d is the thickness of the pyroelectric material.

H = Cp × ρ × A × d (1)

Moreover, the temperature rise ΔT of the pyroelectric body due to absorption of infrared rays can be expressed by the following formula (2) using the heat capacity H described above. Where η is the infrared absorption efficiency, P is the amount of incident infrared rays, and G is the thermal conductance. Further, ω is an angular frequency of the infrared power, and j is a complex symbol.

ΔT = ηP / (jωH + G) (2)

FIG. 4 shows the relationship between the amount of charge generated in the pyroelectric material and the film thickness using the above formulas (1) and (2). The vertical axis represents the amount of charge Qn generated by infrared irradiation, and the horizontal axis represents the pyroelectric film thickness.
Up to a certain film thickness, as the film thickness increases, more infrared rays are absorbed and the temperature rises. Therefore, more polarization inversion occurs and the amount of generated charge increases as shown in FIG.
However, if the film thickness exceeds a certain thickness, the thermal capacity of the pyroelectric material increases, so that the temperature hardly increases and the amount of generated charge decreases.

  Thus, the infrared detection sensitivity cannot be increased simply by increasing the thickness of the pyroelectric material. That is, although it is necessary to consider the temperature rise efficiency of the pyroelectric body, the film thickness (absorption amount of infrared rays) and the temperature rise efficiency of the pyroelectric body are in a trade-off relationship. As shown in FIG. 4, there is an optimum film thickness point at which the amount of generated charge is maximized, and the film thickness of the pyroelectric material is preferably set to this film thickness.

  Furthermore, if the pyroelectric elements are provided with a plurality of upper and lower layers as in the present embodiment, the infrared ray equivalent to increasing the film thickness as a whole without reducing the temperature rise efficiency of the pyroelectric body. Absorption can be obtained. For this reason, in this embodiment, it is possible to increase both the efficiency of raising the temperature of the pyroelectric material and the amount of absorption of infrared rays.

2. First modification (example in which the pyroelectric elements are filled with a thermal insulating layer)
FIG. 5 is a schematic cross-sectional view showing an infrared detection element 200 according to the first modification. Again, for simplicity, only one pixel is shown.
An infrared detection element 200 according to this modification includes a substrate 21 and pyroelectric elements 30, 31, and 32 that are formed on the substrate 21 and generate an electrical signal in response to an increase in temperature.

The pyroelectric element 30 has a spontaneous polarization value that changes as the temperature rises, and generates a surface charge, an upper electrode 23 disposed on the upper surface of the pyroelectric body 22, and a lower surface of the pyroelectric body 22. And a lower electrode 24 to be disposed.
In the present modification, the pyroelectric body 22 is not particularly limited as long as the value of the spontaneous polarization changes as the temperature rises by absorbing infrared rays. For example, lead titanate or lithium tantalate can be used as the inorganic material, and glycine trisulfide (TGS), polyvinylidene difluoride, or the like can be used as the organic material.

  The upper electrode 23 and the lower electrode 24 are preferably made of a conductive material that easily absorbs infrared rays, and assists in increasing the temperature of the pyroelectric material. As this material, for example, chromium can be used.

Also in this modification, the infrared detection element 200 has a multilayer structure in which a plurality of pyroelectric elements 30, 31, and 32 overlap each other, for example. The pyroelectric elements 31 and 32 may be made of the same material as the pyroelectric element 30 described above, or may be made of different materials.
Therefore, among the infrared rays A5 incident on the uppermost pyroelectric element 30, the infrared rays A6 that are not absorbed enter the pyroelectric element 31 and are absorbed here. Infrared light A7 that has also passed through the pyroelectric element 31 can be absorbed again by entering the pyroelectric element 32.

  The lower electrode 25 of the lowermost pyroelectric element 32 is preferably made of a conductive material that reflects infrared rays. Thereby, the infrared rays that have also passed through the pyroelectric element 32 are reflected and enter the pyroelectric elements 32, 31, and 30 again, so that the absorption efficiency can be further increased.

Further, the upper electrode 23 and the lower electrode 24 of the pyroelectric elements 30, 31, 32 are connected to each other by wirings 26, 27, and the pyroelectric elements 30, 31, 32 are connected in series. The wirings 26 and 27 are connected to, for example, a voltage converter and a switching circuit (not shown) disposed in the lower layer of the substrate 21 via vias or the like.
Therefore, the pyroelectric elements 30, 31, and 32 detect infrared rays by taking out, for example, a voltage signal or a current signal from a change in surface charge caused by the temperature rise of the pyroelectric body 22.

  In addition, since the pyroelectric elements 30, 31, and 32 are arranged in the vertical direction, the wirings 26 and 27 can easily connect each other. For this reason, it is not necessary to arrange a voltage converter or a switching circuit for each pyroelectric element, and an increase in the number of parts can be suppressed.

In this modification, the space between the pyroelectric elements 30, 31, 32 and the wirings 26, 27 is filled with a thermal insulating layer 28. For example, in the first embodiment, this portion is made space by etching the sacrificial layer. However, when the S / N ratio of the detected signal can be sufficiently obtained, for example, the sacrificial layer is left as it is, and the thermal insulating layer It is good.
Thus, it is preferable to form the thermal insulating layer because not only the thermal insulating effect but also the mechanical strength can be increased as compared with the case where the thermal insulating layer is formed. As a material of the heat insulating layer, for example, SiO ₂ can be used. In addition, an organic material or the like may be used.

Similarly, in other pixels not shown, pyroelectric elements of each layer are aligned and overlapped in the vertical direction. In pixels adjacent to each other, pyroelectric elements of each layer are arranged in the horizontal direction with the thermal insulating layer 28 interposed therebetween.
In addition, as an insulating layer which fills between the pyroelectric elements of an up-down direction, it is preferable to use the material with the high transmittance | permeability of infrared rays, for example, can use Si and Ge.

As described above, the infrared detection element 200 according to this modification also has a multilayer structure in which pyroelectric elements are stacked one above the other. Accordingly, the infrared light transmitted through the upper layer pyroelectric element is absorbed by the pyroelectric element disposed in the lower layer. For this reason, infrared absorption efficiency can be improved. In FIG. 5, the pyroelectric element has a three-layer structure, but the absorption efficiency can be increased as the number of layers is increased, so the number of layers may be changed as appropriate.
In addition, since the pyroelectric body has a multi-layered structure, the infrared absorption efficiency can be increased without reducing the temperature rise efficiency of the pyroelectric body. Therefore, it is possible to further improve the infrared detection sensitivity by setting the film thickness so that the amount of charge generation of the pyroelectric material is maximized for each layer.

  Further, since the pyroelectric elements 30, 31, and 32 are arranged in the vertical direction, the pyroelectric elements 30, 31, and 32 can be connected in series by simple three-dimensional wirings 26 and 27. Thereby, it is not necessary to arrange | position a voltage converter, a switching circuit, etc. for each pyroelectric element 30,31,32, and the increase in a number of parts can be suppressed.

3. Second Embodiment FIG. 6 is a schematic cross-sectional view showing the structure of an infrared detection element 300 according to a second embodiment. The infrared detecting element 300 according to the present embodiment includes a pyroelectric element including a pyroelectric body 45 that generates an electrical signal in response to a temperature rise. The infrared detecting element 300 includes pyroelectric elements 40 and 41 constituting the first pyroelectric element layer, and a second pyroelectric element layer disposed below the pyroelectric elements 40 and 41. The pyroelectric element 42 is provided. Further, the infrared detection element 300 includes pyroelectric elements 43 and 44 that constitute a third pyroelectric element layer, which is disposed below the pyroelectric element 42.
The pyroelectric element 42 constituting the second pyroelectric element layer is disposed below the gap between the pyroelectric elements 40 and 41 constituting the first pyroelectric element layer.
Further, the pyroelectric elements 43 and 44 constituting the third pyroelectric element layer are directly below the pyroelectric elements 40 and 41 constituting the first pyroelectric element layer and the second pyroelectric element. It arrange | positions under the clearance gap between the pyroelectric elements which comprise a layer.
Further, the space between these pyroelectric elements is made hollow by sacrificial layer etching or the like, and the individual pyroelectric elements are in a thermally independent state.

In the pyroelectric element 40, the value of the spontaneous polarization changes as the temperature rises, generating a surface charge, an upper electrode 47 disposed on the upper surface of the pyroelectric body 45, and a lower surface of the pyroelectric body 45. A lower electrode 46 is provided.
In the present embodiment, the pyroelectric body 45 only needs to absorb polarization and cause a polarization inversion when the temperature rises. Further, it is preferable that the upper electrode 47 and the lower electrode 46 are made of a conductive material that easily absorbs infrared rays, and assists the temperature rise of the pyroelectric material.

Similarly to the pyroelectric element 40, the pyroelectric elements 41, 42, 43, and 44 include a pyroelectric body 45, and an upper electrode 47 and a lower electrode 46 disposed on the upper and lower surfaces thereof. The pyroelectric elements 40 and 44 are aligned and arranged one above the other, and the respective upper and lower electrodes are connected by wiring (not shown).
Similarly, the pyroelectric elements 41 and 43 are also aligned vertically and the upper electrodes 47 and the lower electrodes 46 are connected to each other by wiring.
These wirings are connected to, for example, via a via or the like a voltage converter (not shown) or a switching circuit arranged in the lower layer of the substrate.

Therefore, when the infrared rays A8 and A9 are incident on the pyroelectric elements 40 and 41, the pyroelectric elements 43 and 44 can absorb the infrared rays A10 and A11 that cannot be absorbed by the pyroelectric elements 40 and 41.
In addition, since the pyroelectric body has a multi-layered structure, the infrared absorption efficiency can be increased without reducing the temperature rise efficiency of the pyroelectric body. Therefore, the infrared detection sensitivity can be further improved by setting the film thickness at which the charge generation amount of the pyroelectric material is maximized for each layer.

In the present embodiment, the pyroelectric element 42 is disposed below the gap between the pyroelectric element 40 and the pyroelectric element 41.
In the past, it was not possible to absorb infrared rays incident on the gaps between pixels.
However, in the infrared detecting element 300 according to the present embodiment, the infrared A12 incident on the gap between the pyroelectric element 40 and the pyroelectric element 41 can be absorbed by the pyroelectric element 42. Therefore, the aperture ratio can be set to 1, and the infrared absorption rate can be further increased.
In this way, in the two pyroelectric element layers adjacent to each other in the upper and lower directions, each pyroelectric element of the lower pyroelectric element layer is arranged below the gap between the adjacent pyroelectric element layers of the upper pyroelectric element layer. By adopting such a configuration, the infrared absorption rate can be further increased.

In FIG. 6, three pyroelectric element layers are stacked, but the pyroelectric element layers may be further increased.
Further, a pyroelectric element may be disposed below the pyroelectric element 42 so that infrared rays transmitted through the pyroelectric element 42 are absorbed.

  The lower electrode of the lowermost pyroelectric element is preferably made of a material such as Al that reflects infrared rays. Thereby, the remaining infrared rays that are not absorbed are reflected and can be absorbed by the pyroelectric element in the upper layer.

4). Second Modification FIG. 7 is a schematic cross-sectional view of an infrared detection element 400 according to a second modification.
An infrared detecting element 400 according to this modification includes pyroelectric elements 50 and 51 constituting a first pyroelectric element layer, and a second pyroelectric element layer disposed below the pyroelectric elements 50 and 51. And a pyroelectric element 52. Further, the infrared detecting element 400 includes pyroelectric elements 53 and 54 that constitute a third pyroelectric element layer, which is disposed below the pyroelectric element 52.
The pyroelectric element 52 constituting the second pyroelectric element layer is disposed below the gap between the pyroelectric elements 50 and 51 constituting the first pyroelectric element layer.
Further, the pyroelectric elements 53 and 54 constituting the third pyroelectric element layer are directly below the pyroelectric elements 50 and 51 constituting the first pyroelectric element layer and the second pyroelectric element. It arrange | positions under the clearance gap between the pyroelectric elements which comprise a layer.

In the pyroelectric element 50, the value of the spontaneous polarization changes as the temperature rises, and the pyroelectric body 55 generates surface charges, the upper electrode 57 disposed on the upper surface of the pyroelectric body 55, and the lower surface of the pyroelectric body 55. A lower electrode 56 is provided.
The pyroelectric material 55 may be any material that causes polarization reversal by absorbing infrared rays and increasing its temperature in this modified example. Further, it is preferable that the upper electrode 57 and the lower electrode 56 are made of a conductive material that easily absorbs infrared rays, and assists the temperature rise of the pyroelectric material.

Similarly to the pyroelectric element 50, the pyroelectric elements 51, 52, 53, and 54 include a pyroelectric body 55 and an upper electrode 57 and a lower electrode 56 disposed on the upper and lower surfaces thereof. The pyroelectric elements 50 and 54 are aligned and arranged one above the other, and the upper electrode 57 and the lower electrode 56 are connected to each other by wiring (not shown).
Similarly, the pyroelectric elements 51 and 53 are also aligned vertically and the upper electrodes 57 and the lower electrodes 56 are connected to each other by wiring.
These wirings are connected to, for example, via a via or the like a voltage converter (not shown) or a switching circuit arranged in the lower layer of the substrate.

Therefore, when the infrared rays A13 and A14 are incident on the pyroelectric elements 50 and 51, the pyroelectric elements 53 and 54 can absorb the infrared rays A16 and A17 that cannot be absorbed by the pyroelectric elements 50 and 51.
In addition, since the pyroelectric body has a multi-layered structure, the infrared absorption efficiency can be increased without reducing the temperature rise efficiency of the pyroelectric body. Therefore, the infrared detection sensitivity can be further improved by setting the film thickness at which the charge generation amount of the pyroelectric material is maximized for each layer.

Furthermore, a pyroelectric element 52 is disposed below the gap between the pyroelectric element 50 and the pyroelectric element 51.
Therefore, also in the infrared detecting element 400 according to this modification, the infrared A15 incident on the gap between the pyroelectric element 50 and the pyroelectric element 51 can be absorbed by the pyroelectric element 52. Therefore, the aperture ratio can be set to 1, and the infrared absorption rate can be further increased.
In this way, in the two pyroelectric element layers adjacent to each other in the upper and lower directions, each pyroelectric element of the lower pyroelectric element layer is arranged below the gap between the adjacent pyroelectric element layers of the upper pyroelectric element layer. By adopting such a configuration, the infrared absorption rate can be further increased.

Here, the pyroelectric element layers are stacked in three layers, but the pyroelectric element layers may be further increased.
Further, a pyroelectric element may be disposed below the pyroelectric element 52 so that infrared rays transmitted through the pyroelectric element 52 are absorbed.
The lower electrode of the lowermost pyroelectric element is preferably made of a material such as Al that reflects infrared rays. Thereby, the remaining infrared rays that are not absorbed are reflected and can be absorbed by the pyroelectric element in the upper layer.

In the present modification, the pyroelectric elements are filled with the thermal insulating layer 61. In the second embodiment (FIG. 6), this portion is made hollow by sacrificial layer etching or the like. However, if a sufficient S / N ratio of the detected signal can be obtained, it is left as it is for thermal insulation. It may be a layer. As such a material, for example, SiO ₂ can be used, and other resin materials may be used.
In addition, as the insulating layer filling the space between the pyroelectric elements in the vertical direction, it is preferable to use a material having a high infrared transmittance. For example, Si or Ge can be used.

  As in this modification, filling the space between the pyroelectric elements with a heat insulating material is preferable because not only the pyroelectric elements are thermally independent but also the mechanical strength of the infrared detecting element 400 can be increased. .

5. Third embodiment (example of infrared detection device)
Next, an example in which the infrared detection element described so far is applied to an electronic device such as an infrared imaging device will be described below with reference to FIG.
FIG. 8 is a schematic configuration diagram showing the configuration of the infrared detecting device 500 according to the present embodiment. The infrared detection apparatus 500 according to the present embodiment includes a light collecting unit 70 that collects infrared light from an imaging target, and an infrared detection element 71 that receives the infrared light collected by the light collecting unit 70.
Also, a chopper drive circuit 72 that determines the angular frequency of the infrared rays incident on the infrared detection element 71, a control circuit 73 that controls the charge output by the infrared irradiation to the infrared detection element 71, and the infrared detection element 71 A signal processing circuit 74 for processing the output signal is provided.

The condensing part 70 will not be specifically limited if it condenses the infrared rays etc. from an imaging object, and makes it image-form. One lens may be included, and two or more lenses may be included.
For example, conventionally proposed lenses include Ge lenses and Si lenses.

The infrared light collected by the light collecting unit 70 is received by the infrared detection element 71, and an image to be imaged is acquired. The infrared detection element 71 includes the infrared detection elements 100 to 400 shown in the first to second embodiments and the first to second modifications (FIGS. 1, 5, 6, and 7). Composed.
The infrared detection element 71 is provided with a charge / voltage conversion circuit, a noise correction circuit, and an analog / digital conversion circuit as necessary.

  Therefore, the infrared detection device 500 according to the present embodiment has a configuration in which a plurality of pyroelectric elements are arranged in the vertical direction in the infrared detection element 71. For this reason, the infrared rays that could not be absorbed by one layer of pyroelectric elements can be absorbed by the pyroelectric elements arranged in the lower layer.

The drive circuit 72 modulates infrared rays by driving a chopper (not shown), for example, and causes infrared rays having a specific angular frequency to enter the infrared detection element 71. The chopper may be a mechanism that periodically blocks incident infrared rays, for example. For example, a mechanically moving shutter mechanism may be used, and a configuration in which an opening for irradiating a part of pixels with electromagnetic waves may be arbitrarily set like a liquid crystal shutter.
The control circuit 73 includes a timing generator such as a start pulse and a clock pulse, for example, and controls accumulation, discharge, etc. of charges generated by infrared irradiation.

  In addition, the signal processing circuit 74 performs signal processing such as correlated double sampling on the output signal from the infrared detection element 71 and records it on a recording medium such as a memory or outputs it to a monitor such as a liquid crystal display. To do.

  Thus, in infrared detecting device 500 according to the present embodiment, pyroelectric elements are arranged in a plurality of layers in the vertical direction in infrared detecting element 71 that receives infrared rays from an imaging target. For this reason, the infrared rays that have passed through the first pyroelectric element can be absorbed by the pyroelectric element disposed in the lower layer. Therefore, it is possible to increase the infrared absorption rate, and it is possible to perform infrared imaging with higher sensitivity.

  The embodiments of the infrared detection element and the infrared detection device according to the present invention have been described above. The present invention is not limited to the above-described embodiment, and it is needless to say that the present invention includes various conceivable forms without departing from the gist of the present invention described in the claims.

  1, 13, 21, ... substrate, 2, 14, 22, 45, 55 ... pyroelectric material, 3, 15, 23, 47, 57 ... upper electrode, 4, 16, 24, 46, 56 ... Lower electrode, 5, 25 ... Electrode, 6, 7, 26, 27, 48, 49, 58, 59 ... Wiring 10, 11, 12, 30, 31, 32, 40, 41, 42, 43, 44, 50, 51, 52, 53, 54, 110 ... pyroelectric elements, 28, 61 ... thermal insulation layer, 70 ... light condensing part, 72 ... drive circuit, 73 ... Control circuit, 74 ... Signal processing circuit, 71, 100, 200, 300, 400 ... Infrared detector, 500 ... Infrared detector

Claims (8)

A pyroelectric material that changes its spontaneous polarization value due to an increase in temperature and generates a surface charge; an upper electrode disposed on the upper surface of the pyroelectric material; and a lower electrode disposed on the lower surface of the pyroelectric material. Including two or more pyroelectric element layers in which pyroelectric element layers made of electric elements are arranged above and below,
Infrared detector. Each pyroelectric element layer of each layer is composed of a plurality of pyroelectric elements arranged in the horizontal direction,
In the two adjacent pyroelectric element layers in the upper and lower directions, each of the pyroelectric elements in the lower pyroelectric element layer is disposed below the gap between adjacent pyroelectric elements in the upper pyroelectric element layer. The infrared detection element according to claim 1.   The infrared detection element according to claim 1, further comprising a heat insulating material buried in a side surface of each pyroelectric element and a gap between the pyroelectric elements.   The infrared detection element according to claim 3, wherein the thermal insulating material buried in a gap between the pyroelectric elements in the vertical direction is Si or Ge.   The infrared detection element according to claim 1, wherein the lower electrode of the pyroelectric element of the pyroelectric element layer disposed in the lowermost layer is formed of a conductive material that reflects infrared light.   The infrared detection element according to claim 5, wherein a lower electrode of the pyroelectric element of the pyroelectric element layer disposed in the lowermost layer is formed of Al.   The infrared detection element according to claim 1, wherein the pyroelectric elements of each pyroelectric element layer are arranged in the vertical direction. A condensing unit for condensing infrared rays from the imaging target;
A pyroelectric material that changes its spontaneous polarization value due to an increase in temperature and generates a surface charge; an upper electrode disposed on the upper surface of the pyroelectric material; and a lower electrode disposed on the lower surface of the pyroelectric material. An infrared detecting element that includes two or more pyroelectric element layers, each including a pyroelectric element layer made of an electric element, and that receives infrared rays collected by the light collecting unit;
A control circuit for controlling the charge output from the infrared detection element;
A signal processing circuit for processing an output signal from the infrared detection element;
Infrared detector equipped with.

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