Photoelectric conversion element, infrared sensor, infrared image sensor, infrared camera, millimeter-wave radar, millimeter-wave two-dimensional radar, and photoelectric conversion method

Abstract

A photoelectric conversion element 10 is provided with: a photoelectric conversion part 1 formed, using a polar material having a crystal structure with a broken spatial inversion symmetry, so as to include an irradiation surface 1a for receiving incident light having an energy smaller than the bandgap of the polar material; and electrodes 2, 3 positioned on the photoelectric conversion part 1 or at the end parts of the photoelectric conversion part 1 at a distance from each other so as to sandwich the irradiation surface 1a. The irradiation surface 1a receives incident light having an energy corresponding to the phonon energy of the polar material of the photoelectric conversion part 1.

Description

Technical Field

[0001] The present invention relates to a photoelectric conversion element and method for generating a current (hereinafter referred to as a phonon shift current) in a photoelectric conversion unit by irradiating the photoelectric conversion unit with light energy equivalent to the phonon energy of a photoelectric conversion unit material, and extracting this phonon shift current from opposing electrodes provided in the photoelectric conversion unit, and also to a sensor technology using the photoelectric conversion element.

Background Art

[0002] Conventionally, a general photoelectric conversion unit includes a p-type semiconductor and an n-type semiconductor. An internal electric field is generated in the photoelectric conversion unit by the p-n junction of the p-type semiconductor and the n-type semiconductor. When incident light enters this photoelectric conversion unit, electrons jump from the valence band to the conduction band, generating a pair of electrons and holes. This pair of electrons and holes move and separate to the p-type side and the n-type side, respectively, due to the internal electric field. Thereby, a current can be extracted from the photoelectric conversion unit. In recent years, a photoelectric conversion element using a band excitation shift current that does not use such a p-n junction has been invented, and research and development have been in full swing (see, for example, Patent Document 1 and Non-Patent Documents 1 to 3). Patent Document 1 Japanese Patent Application Laid-Open No. 2019-121687 Non-Patent Document 1 S. M. Young and A. M. Rappe, "First Principles Calculation of the Shift Current Photovoltaic Effect in Ferroelectrics", Physical Review Latters 109, 116601 (2012). Non-Patent Document 2 M. Sotome, M. Nakamura, J. Fujioka, M. Ogino, Y. Kaneko, T. Morimoto, Y. Zhang, M. Kawasaki, N. Nagaosa, Y. Tokura, and N. Ogawa, "Spectral dynamics of shift current in ferroelectric semiconductor SbSI", Proc. Natl. Acad. Sci. 116, 1929 (2019). Non-Patent Document 3 M. Sotome, M. Nakamura, J. Fujioka, M. Ogino, Y. Kaneko, T. Morimoto, Y. Zhang, M. Kawasaki, N. Nagaosa, Y. Tokura, and N. Ogawa, "Ultrafast spectroscopy of shift-current in ferroelectric semiconductor Sn2P2S6", Appl. Phys. Lett. 114, 151101 (2019). Non-Patent Document 4 J. Hlinka, T. Ostapchuk, D. Nuzhnyy, J. Petzelt, P. Kuzel, C. Kadlec, P. Vanek, I. Ponomareva, and L. Bellaiche, "Coexistence of the Phonon and Relaxation Soft Modes in the Terahertz Dielectric Response of Tetragonal" Physical Review Latters 101, 167402 (2008). Non-Patent Document 5: Takuya Hoshina, Kazuki Kanehara, Hiroaki Takeda, and Takaaki Tsurumi, "Terahertz dielectric response of single-domain BaTiO3 measured by far-infrared spectroscopic ellipsometry", Japanese Journal of Applied Physics 53, 09PD03 (2014).

Summary of the Invention

Problems to be Solved by the Invention

[0003] A photoelectric conversion element using a conventional band excitation shift current (Patent Document 1 and Non-Patent Documents 1 to 3) is a photoelectric conversion element based on a completely new principle that does not require the conventional p-n junction. Since it is a conversion element that does not involve dissipation such as the mobility, impurities, and heat of the material of the photoelectric conversion element, it can provide an ultra-high-speed and thermal-noise-free high-sensitivity conversion element. However, the excitation light energy used in the conventional band excitation shift current requires light energy equal to or higher than the band gap energy of the conversion element material. For this reason, it has been difficult to find a material with a small band gap energy of the photoelectric conversion element material in order to improve the light conversion efficiency for detecting infrared light and the like.

[0004] An infrared sensor can measure the temperature of a measurement object. The wavelength range of the infrared light radiated from the measurement object follows Planck's radiation law. Objects with temperatures ranging from near room temperature to several hundred degrees emit infrared light in a wavelength range of about 3 μm to 30 μm. Therefore, an infrared sensor needs to have sensitivity in the wavelength range of 3 μm to 30 μm. Furthermore, in the wavelength range of the infrared light, it is necessary to have sensitivity in a region where absorption by moisture and carbon dioxide in the atmosphere is low (atmospheric window). Therefore, an infrared sensor needs to have sensitivity at wavelengths in the N band (7.5 - 14.5 μm) or Q band (17 - 25 μm) of the atmospheric window. Materials having sensitivity in this wavelength range are, for example, HgCdTe. HgCdTe has sensitivity at 12 μm (100 meV), but HgCdTe elements cannot be used unless cooled to an extremely low temperature of 77 K. When the element temperature is at room temperature, a large amount of thermal noise is generated in the output signal, and the effective infrared signal component from the measurement object cannot be extracted. Therefore, for room-temperature infrared sensors that do not require cooling, bolometers are used. Bolometers have sensitivity in the range of 3 μm to 30 μm. Bolometers measure infrared light as a change in resistivity caused by minute heat generation due to infrared incident light on a VOx or amorphous silicon material. Room-temperature bolometers have made remarkable technological progress in recent years, such as adopting a thin-film structure to improve sensitivity. However, room-temperature bolometers have limitations such as the size of the bolometer element cannot be reduced to ensure sensitivity. There are also many problems to be overcome, such as large thermal noise, the need to control temperature fluctuations of the bolometer element, and slow detection speed (image afterimage effect).

[0005] Millimeter-wave radar is an essential device for the automated driving of vehicles. Millimeter-wave radar needs to have sensitivity in the wavelength range of 20 GHz (15 mm) to 100 GHz (3 mm). In this region, the detection device is exclusively a waveguide (the container in the waveguide is filled with air). The waveguide requires a size of about several centimeters on each side, making it difficult to install on the front part of the vehicle. Furthermore, the sensitivity is low, and various noise countermeasures are required. It is not compatible with the miniaturization technology of peripheral devices constituting the electronic circuit. There were many such significant problems to be overcome.

Means for Solving the Problems

[0006] In a first aspect of the present invention, a photoelectric conversion unit is formed using a polar material having a crystal structure with broken space inversion symmetry, and includes an irradiation surface that receives incident light having an energy smaller than the bandgap of the polar material. A first electrode and a second electrode are disposed at an end of the photoelectric conversion unit or on the photoelectric conversion unit with an interval therebetween across the irradiation surface. A filter that extracts the wavelength of the light to be measured is provided, and a photoelectric conversion element is provided.

[0007] In a second aspect of the present invention, an infrared sensor is provided that includes the photoelectric conversion element of the first aspect, a current detection unit that detects the intensity of infrared rays received at the irradiation surface by a current extracted from the first and second electrodes, and a detection signal display unit that displays a detection signal.

[0008] In a third aspect of the present invention, a plurality of the photoelectric conversion elements of the first aspect are provided, the plurality of photoelectric conversion elements are arranged in a two-dimensional plane, the surfaces of the photoelectric conversion units of the photoelectric conversion elements are arranged in a two-dimensional plane, and a plurality of current detection units that detect the intensity of two-dimensional infrared rays received at the plurality of irradiation surfaces of the plurality of photoelectric conversion elements by currents extracted from a plurality of pairs of opposing electrodes provided in the plurality of photoelectric conversion elements, and an infrared image sensor that sequentially outputs a two-dimensional detection signal are provided.

[0009] In a fourth aspect of the present invention, an infrared camera is provided that includes the infrared image sensor of the third aspect, a detection signal display unit that sequentially extracts a two-dimensional detection signal from the infrared image sensor and displays it as a two-dimensional image, and a detection signal storage unit that sequentially stores the two-dimensional detection signal.

[0010] In a fifth aspect of the present invention, a millimeter-wave radar is provided that includes the photoelectric conversion element of the first aspect, a current detection unit that detects the intensity of millimeter waves received at the irradiation surface by a current extracted from the first and second electrodes, and a detection signal display unit that displays a detection signal.

[0011] In a sixth aspect of the present invention, a plurality of the photoelectric conversion elements of the first aspect are provided, the plurality of photoelectric conversion elements are arranged in a two-dimensional plane, and the intensity of the two-dimensional millimeter wave received on the plurality of irradiation surfaces of the plurality of photoelectric conversion elements is detected by currents taken out from a plurality of pairs of opposing electrodes provided on the plurality of photoelectric conversion elements. A millimeter-wave two-dimensional radar is provided, which includes a plurality of current detection units, a detection signal display unit that sequentially displays a two-dimensional detection signal, and a detection signal storage unit that sequentially stores the two-dimensional detection signal.

[0012] In a seventh aspect of the present invention, a step of irradiating an irradiation surface of a photoelectric conversion unit formed using a polar material having a crystal structure with broken space inversion symmetry with irradiation light having an energy smaller than the bandgap of the polar material, and a step of extracting the current generated in the photoelectric conversion unit from an end of the photoelectric conversion unit or from first and second electrodes arranged with a space therebetween with the irradiation surface interposed therebetween on the photoelectric conversion unit are provided.

Advantages of the Invention

[0013] According to the present invention, a current flows with irradiation light whose energy received on the irradiation surface of the photoelectric conversion unit is smaller than the band gap (also referred to as band gap) of the polar material. A current generated with irradiation light energy of lower energy can be extracted as compared with a current using a conventional p-n junction that requires band gap energy and a conventional band excitation shift current. In particular, by receiving light irradiation having energy corresponding to the phonon energy of the polar material on the irradiation surface, a phonon shift current can be utilized. Here, a phonon (also referred to as a phonon) is a quantum of lattice vibration in a crystal, and a shift current refers to a direct current flowing without applying an external electric field by irradiating a substance having no space inversion symmetry with light. A phonon shift current refers to a shift current generated due to excitation of the phonon mode of the polar material by irradiation light and electron-lattice interaction. Since this phonon shift current does not depend on the mobility of electrons, an ultra-high speed response is possible. Since the phonon shift current is not accompanied by heat dissipation, it does not generate thermal noise. A current due to the phonon shift current can be extracted from the photoelectric conversion unit with ultra-high speed, low thermal noise, and high sensitivity.

[0014] The photoelectric conversion element of the present invention can extract a current with irradiation light having energy equivalent to the phonon energy existing in the photoelectric conversion element material. The energy of phonons existing in the photoelectric conversion element material exists in the energy region of far-infrared to infrared light from the order of 10 GHz band of 0.08 meV (15 mm) to 117 meV (10 μm). The types of existing phonon modes and the energy of each mode differ depending on the material of the photoelectric conversion unit.

[0015] For practical use in an infrared sensor, it is necessary to be able to detect infrared rays in the N band or Q band region, which is a region where the atmosphere is transparent. There exists a material having the wavelength of a phonon having this infrared wavelength. As shown in the examples, the relaxation mode of BaTiO3 has a wavelength of 19.2 μm and has a wavelength in the Q band region. That is, a current due to the phonon shift current by infrared incident light can be extracted from the photoelectric conversion unit with ultra-high speed, low thermal noise, and high sensitivity.

[0016] For practical use in in-vehicle radars, it is necessary to be able to detect millimeter waves in the range from 20 GHz (wavelength 15 mm) to 100 GHz (wavelength 3 mm). There are materials that have phonons of millimeter waves in this range. As shown in the examples, the soft mode of BaTiO3 has a wavelength from 1 mm to 15 mm. That is, the current due to phonon shift current can be extracted from the photoelectric conversion section with ultra-high speed, low thermal noise, and high sensitivity by millimeter wave incident light.

[0017] According to an example of typical ferroelectric BaTiO3, the conversion efficiency of phonon shift current is about the same as or higher than that of conventional band excitation shift current. This result can provide a sensor with excellent sensitivity in the wavelength range from several 10 GHz bands to far-infrared to infrared light. Phonon shift current does not depend on the electron mobility of the material in principle from the generation mechanism. It does not generate electron disturbances due to heat and impurity scattering. Therefore, it provides an epoch-making sensor with ultra-high speed, noise-free, and high-sensitivity response performance. The photoelectric conversion element of the present invention can operate at room temperature as shown in the example BaTiO3. BaTiO3 can operate from room temperature to a high temperature of 120 °C.

[0018] Note that the above summary of the invention does not list all the features of the present invention. Also, sub-combinations of these feature groups can also be inventions.

Brief Description of the Drawings

[0019]

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Mode for Carrying Out the Invention

[0020] Embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals are given to the common parts in each figure, and duplicate explanations are omitted. Further, the following description does not limit the invention described in the claims. For example, the present invention is not limited to those provided with all the components described below.

[0021] <Outline of the photoelectric conversion element> FIG. 1 is a configuration diagram of a photoelectric conversion element 10 according to an embodiment of the present invention. The photoelectric conversion element 10 includes a photoelectric conversion unit 1, an irradiation surface 1a, electrodes 2 and 3, and a filter element 6.

[0022] The photoelectric conversion unit 1 is made of a polar material. The polar material is a material having a crystal structure in which space inversion symmetry is broken. The polar material may be a polarized material. For example, the polar material may be a pyroelectric material, a ferroelectric material, or a multilayer film. Note that the photoelectric conversion unit 1 may be formed of a single polar material. Here, the "single polar material" means a material having a crystal structure in which atoms or molecules are regularly arranged and may not contain material components that do not correspond to this arrangement. For example, the "single" may mean that when the polar material is any of the specific examples described later, the photoelectric conversion unit 1 does not contain materials other than the specific example.

[0023] The crystal structure of the photoelectric conversion unit 1 has broken space inversion symmetry. This means that when the crystal structure of the photoelectric conversion unit 1 is mirror-inverted, the structure before mirror inversion does not match the structure after mirror inversion. The photoelectric conversion unit 1 has a structure in which space inversion symmetry is broken in at least one direction (the left-right direction in FIG. 1). In this case, no matter which position in the said direction is the reference point of mirror inversion (the position of the mirror for mirror inversion), the structure before mirror inversion does not match the structure after mirror inversion. Note that since the photoelectric conversion unit 1 is formed of a polar material, as described above, the space inversion symmetry of its crystal structure is broken. Also, the photoelectric conversion unit 1 does not have a p-n junction.

[0024] The photoelectric conversion unit 1 is provided with an irradiation surface 1a on one of its surfaces (the upper surface in this embodiment) for receiving incident light. The irradiation surface 1a can receive light irradiation having energy smaller than the bandgap of the polar material by a filter element 6 described later.

[0025] The electrodes 2 and 3 (examples of the first and second electrodes, respectively) are for extracting the phonon shift current generated in the photoelectric conversion unit 1 to the outside by incident light having an energy equivalent to the energy of the specific phonons of the material of the photoelectric conversion unit 1 to the photoelectric conversion unit 1. The electrodes 2 and 3 are arranged with an interval therebetween across the irradiation surface 1a on the upper surface of the photoelectric conversion unit 1. Note that the electrodes 2 and 3 may be arranged at the ends of the photoelectric conversion unit 1. A metal wire 4 and a metal wire 5 are connected to the electrodes 2 and 3, respectively. The current generated in the photoelectric conversion unit 1 flows through the metal wire 4 and the metal wire 5 via the electrodes 2 and 3.

[0026] The electrodes 2 and 3 are provided in the photoelectric conversion unit 1 and arranged at an interval from each other. Hereinafter, the direction in which the electrodes 2 and 3 are separated from each other is referred to as the electrode separation direction. The electrodes 2 and 3 may be in direct contact with the photoelectric conversion unit 1. In the electrode separation direction, the structure of the photoelectric conversion unit 1 has broken spatial inversion symmetry. Also, the photoelectric conversion unit 1 may be polarized in the electrode separation direction.

[0027] The filter element 6 is an optical element that cuts light irradiation having an energy of at least the band gap of the polar material. In the present embodiment, it is arranged between the electrodes 2 and 3 on the irradiation surface 1a of the photoelectric conversion unit 1. A part of the electrodes 2 and 3 may be stacked and arranged on the ends of the filter element 6 provided on the irradiation surface 1a of the photoelectric conversion unit 1. The filter element 6 may be arranged at an arbitrary position on the optical axis of the incident light. The filter element 6 may be, for example, an element configured by stacking a plurality of birefringent plates and further a phase plate. The filter element may be a band-pass filter that extracts only specific phonon energy. Since the filter element 6 is provided on the irradiation surface 1a, light having an energy of at least the band gap of the polar material among the energy contained in the incident light is thereby cut, and light having an energy smaller than that, particularly light having an energy corresponding to the phonon energy of the polar material of the photoelectric conversion unit 1, is transmitted and can be received by the irradiation surface 1a.

[0028] In addition, when using BaTiO3, which is a ferroelectric material, as the polar material, the filter element 6 may be configured to transmit light with a wavelength of 3 mm to 15 mm or a wavelength of 17 μm to 22 μm. Thereby, the irradiation surface 1a can receive incident light with a wavelength of 3 mm to 15 mm or a wavelength of 17 μm to 22 μm.

[0029] In addition, the current generated in the photoelectric conversion unit 1 is detected by the current detection unit 101. The current detection unit 101 has, for example, an ammeter, and in the example of FIG. 1, the metal wire 4 and the metal wire 5 are connected thereto. The ammeter has a load resistor and displays the voltage generated across both ends of this load resistor. Thereby, the phonon shift current is displayed.

[0030] In addition, the energy and absorption intensity of the phonon mode that generates the phonon shift current differ depending on the material of the photoelectric conversion unit 1. The greater the absorption intensity of the phonon, the greater the phonon shift current intensity. However, it should be noted that if the absorption intensity is too large, the penetration length of the incident light into the material will be short. When the material of the photoelectric conversion unit 1 does not have space inversion symmetry, basically, incident light of all phonon modes can generate a phonon shift current. Strictly speaking, if the tensor component of the phonon mode has the electric field component of the incident light, a phonon shift current is generated.

[0031] <Specific examples of polar materials> The polar material forming the photoelectric conversion unit 1 may be a ferroelectric material. This ferroelectric material is, for example, SbSI, BiSI, TTF-CA (tetrathiafulvalene - p - chloranil), TTF - BA (tetrathiafulvalene - bromanil), BiFeO3, TMB - TCNQ (tetramethylbenzidine - tetracyano quinodimethane), GeTe, CH3NH3PbI3, (2 - (ammoniomethyl)pyridinium)SbI5, Sn2P2S6, BaTiO3, PbTiO3, Pb5Ge3O 11, may be PZT (lead zirconate titanate), LiNbO3, LiTaO3, KNbO3, or KDP (Potassium Dihydrogen Phosphate).

[0032] The polar material forming the photoelectric conversion unit 1 may be a pyroelectric material. The crystal structure of the pyroelectric material does not have space inversion symmetry. It has polarization in all temperature ranges including room temperature. It is a solid electronic material whose polarization transition temperature (Curie temperature) is equal to or higher than the melting temperature or decomposition temperature of the crystal. This pyroelectric material may be, for example, GaFeO3, CdS, GaN, ZnO, CdTe, BiTeI, or BiTeBr.

[0033] The polar material forming the photoelectric conversion unit 1 may be a laminated thin film formed by laminating an A layer, a B layer, and a C layer with different crystal materials in this order. It may also be a structure in which the ABC layers are laminated N times (N is an integer of 1 or more). The laminated film formed by laminating the A layer, the B layer, and the C layer with different crystal materials in this order does not have space inversion symmetry in the lamination direction. This ABC laminated film has polarization in all temperature ranges including room temperature. Each of the A layer, the B layer, and the C layer is an atomic layer thin film having a nano-order thickness. Here, the atomic layer thin film may be a single crystal. The combination of the crystal materials of the A layer, the B layer, and the C layer may be, for example, a combination of LaAlO3, LaFeO3, and LaCrO3, or a combination of CaTiO3, BaTiO3, and SrTiO3. That is, in an example of the former combination, the A layer is made of LaAlO3, the B layer is made of LaFeO3, and the C layer is made of LaCrO3.

[0034] When the polar material forming the photoelectric conversion unit 1 is a pyroelectric material and an ABC laminated film, it has the merit that it is not necessary to apply a voltage (poling process) to align the polarization. The space inversion symmetry of the crystal structure has already been broken at the temperature having the crystal structure. In FIG. 1, the electrodes 2 and 3 may be arranged so as to face these polarization directions.

[0035] Hereinafter, the photoelectric conversion element 10 according to the embodiment of the present invention will be described in more detail.

[0036] <Example 1: Polarization of ferroelectric material BaTiO3> FIG. 2 shows a wiring diagram when a voltage is applied in the poling process of the ferroelectric BaTiO3. It is a wiring diagram for aligning the polarization direction that spontaneously occurs below the Curie temperature in the electrode separation direction. When the temperature of the ferroelectric material is below its Curie temperature, it spontaneously generates polarization in the (100) direction and becomes a ferroelectric. The Curie temperature of the ferroelectric material BaTiO3 is around 395K. The left - right direction in FIG. 1 is the electrode separation direction. The (100) direction of the BaTiO3 single crystal is set in the electrode separation direction (left - right direction) of FIG. 2, and electrodes 2 and 3 are formed at both ends thereof. The electrodes are arranged to face each other in the (100) direction. A predetermined voltage is applied in this arrangement. The polarization aligns in the (100) direction. In the case of BaTiO3, if the electric field for aligning the polarization is 2 - 3 KV / cm or more, the polarization is almost 100% aligned. If the electric field is smaller, the alignment ratio of the polarization decreases. The electrode directions do not have to face each other in the (100) direction. In that case, a larger electric field is required to align 100% of the polarization. In a ferroelectric, applying a voltage to align the polarization is called the poling process.

[0037] FIG. 3 shows the temperature dependence of the polarization when positive and negative electric fields are applied to the photoelectric conversion unit 1. The method of applying a positive electric field to the photoelectric conversion unit 1 is to apply a positive voltage to electrode 2 with respect to electrode 3 as a reference. When a positive electric field is applied to the photoelectric conversion unit 1, the polarization shows a positive value (right - hand direction). When a negative electric field is applied to the photoelectric conversion unit 1, the polarization shows a negative value (left - hand direction). This shows that the polarization direction aligns with the electric field direction. The ferroelectric material BaTiO3 does not generate polarization at temperatures of 395K or higher. It shows that polarization occurs in the electric field direction at temperatures below the Curie temperature of 395K. As shown in FIG. 3, around room temperature of 300K in a BaTiO3 single crystal, it is 60 millicoulombs (m 2It shows a large charge accumulation amount (around). The BaTiO3 single crystal exhibits the characteristics of a ferroelectric material with a large dielectric constant. Fig. 4 shows a crystal model indicating the positions of the constituent atoms of BaTiO3. When there is a polarization P aligned in the (100) direction, the displacement directions of the constituent atoms are indicated by arrows. One Ti atom present at the center of the unit cell of the crystal shifts in the positive direction (rightward) in the (100) direction from the reference point, and six oxygen atoms are displaced from the reference point in the negative direction (leftward) in the (100) direction. The polarization vector P, which is the sum of these displacement vectors, has a value in the (100) direction (rightward). The crystal with polarization in the (100) direction has broken left - right space inversion symmetry. When the Ti atom and oxygen atoms are at the reference point (when the polarization is zero), the left - right inversion symmetry of the crystal is preserved. The existence of polarization is synonymous with the breaking of space inversion symmetry. Polarization occurs below the temperature Tc. The polarization generated in the single crystal aligns within regions of several micrometers (domains). The entire crystal becomes an aggregate of a large number of domains with different polarization directions. It is necessary to apply an electric field to align the polarization in one direction throughout the crystal. The temperature at which the electric field is applied can be any temperature below Tc. Once the polarization is aligned once, thereafter, even after the electric field application is stopped, the polarization direction of the photoelectric conversion unit 1 is maintained in one direction (hysteresis characteristic).

[0038] <Example 2: Measurement Results of Phonon Shift Current in Ferroelectric Material BaTiO3> Example 2 of the photoelectric conversion element 10 according to an embodiment of the present invention will be described with reference to FIGS. 5 and 6. The polar material forming the photoelectric conversion unit 1 is a BaTiO3 crystal which is a ferroelectric. FIG. 6 shows a photograph of the arrangement of the BaTiO3 single crystal, electrode 2, and electrode 3 used in the example. The surface of the BaTiO3 single crystal is the

[0001] plane. The crystal axis (100) direction of the BaTiO3 single crystal is shown in the figure. Electrodes 2 and 3 are provided to face each other in the crystal axis (100) direction of BaTiO3. The materials of electrodes 2 and 3 are a metal laminated film of Au(30 nm) / Ti(20 nm) and are formed by a sputtering apparatus. In the experimental arrangement shown in FIG. 2, a high voltage is applied in the crystal axis (100) direction to align the polarization in the (100) direction in the electrode direction of (100). After polarization formation, metal wires 4 and 5 are connected to the current detection unit 101. In the example of FIG. 5, an oscilloscope 102 is connected to the current detection unit 101. Incident light is incident on the irradiation surface 1a. The phonon shift current generated by the incident light is output as a voltage by the current detection unit 101. The output voltage is displayed on the oscilloscope 102. The incident light is incident perpendicularly to the crystal plane

[0001] . The electric field direction of the incident light is incident parallel to the polarization direction (100). The incident light used at this time is shown in FIGS. 7A and 7B. The energy of the incident light is 0 to 8 meV and is an ultrashort pulse with a time width of 2 picoseconds (2×10 -12 seconds). The band gap of BaTiO3 is around 3.5 eV. Excitation light with an energy smaller by three digits or more is used.

[0039] In Fig. 8, the horizontal axis shows the time response of the phonon shift current at 297 K. A signal intensity of 6 μA is obtained at the peak value. The response time also shows a fast response of 10 nanoseconds. In the case of positive polarization, the phonon shift current is a positive value. When the polarization direction is negative, the phonon shift current flows in the negative direction. As shown by the dashed line, the phonon shift current does not flow at 413 K above Tc. Polarized BaTiO3 has been demonstrated to generate a phonon shift current that depends on the polarization direction with incident light of a small energy below the band gap. The 10-nanosecond response time shown here is limited to a response time on the order of 10 nanoseconds of the differential amplification circuit of the operational amplifier used in the experiment. If observed with a differential amplification high-speed device such as GaAs, it can be demonstrated that the response is ultra-fast at about 2 picoseconds of the excitation light. In fact, the emission time measurement results from the shift current without using electrodes have demonstrated that the emission time of the band-excited shift current is a response of several picoseconds (see Non-Patent Documents 2 and 3). Since the shift current is a current that does not depend on the mobility of electrons in the crystal in principle, it can respond ultra-fast. It can be expected that the phonon shift current also has an ultra-fast response of several picoseconds.

[0040] Compare the band-excited shift current intensity with the phonon shift current of 6 μA at 297 K in Fig. 8 with a pulse width of 5 nanoseconds and an irradiation area of 1 mm 2 The phonon shift current per unit watt of incident light is I P ZZZ = J / P = (6 μA * 5 ns * 1 mm 2 ) / (0.1 mW / 1 kHz) = 0.3 * 10 -12 A·m 2 / W and is obtained. According to Non-Patent Document 1, the band-excited shift current per unit watt of incident light is I B ZZZ = J / P = 0.6 pA / (0.5 mW / cm 2 ) = 0.12 * 10 -12 A·m 2 / W is. The phonon shift current IP The intensity is the band excitation shift current I B It is surprising that it has an intensity approximately the same as or greater than that. In terms of photosensitivity, the phonon shift current has been shown to have the same photosensitivity as the band excitation shift current.

[0041] The phonon shift current can be represented by the general formula (1).

Equation

[0042] <Example 3: Measurement Results of Phonon Shift Current in Ferroelectric Material BaTiO3> Example 3 of the photoelectric conversion element 10 according to an embodiment of the present invention will be described with reference to FIG. 10. In this Example 3, the polar material forming the photoelectric conversion unit 1 is BaTiO3 crystal, which is a ferroelectric. The materials for forming the electrodes 2 and 3 are Au / TiN. The electrode material is a metal laminated film of Au (30 nm) / Ti (20 nm), which is formed by a sputtering apparatus in the same manner as in Example 2. In the experimental arrangement shown in FIG. 2, a high voltage is applied in the direction of the crystal axis (100), and the polarization is aligned in the (100) direction in the (100) electrode direction. After the polarization is formed, metal wires 4 and 5 are connected to the electrodes 2 and 3 in FIG. 10. The current generated in the photoelectric conversion unit 1 flows through the metal wires 4 and 5. The metal wires 4 and 5 are connected to two input terminals of a galvanometer included in the current detection unit 101. The voltage output from the current detection unit 101 is displayed on the oscilloscope 102. The incident light is incident perpendicularly to the crystal plane

[0001] . The electric field direction of the incident light is incident perpendicularly to the polarization direction (100). The incident light used at this time is shown in FIGS. 7A and 7B. The energy of the irradiated light is 0 to 8 meV, and it is an ultrashort pulse with a time width of 2 picoseconds (10 -12 seconds). The band gap of BaTiO3 is around 3.5 eV. Excitation light with an energy three or more digits smaller is used.

[0043] In FIG. 11, the horizontal axis shows the time response at 297 K of the phonon shift current. A signal intensity of 4 μA is obtained at the peak value. The response time also shows a fast response of 10 nanoseconds. In the case of positive polarization, it is a positive phonon shift current. In the case of negative polarization, it is a negative phonon shift current. As shown by the broken line, the phonon shift current does not occur at 413 K or higher than Tc without polarization. It has been demonstrated that BaTiO3 with polarization generates a phonon shift current depending on the polarization direction with a small energy below the band gap even when the electric field component of the incident light is perpendicular to the polarization. The fact that this response time is limited to the response time of the differential amplifier circuit used in the experiment, which is on the order of 10 nanoseconds, was explained in Example 2. The response time of the phonon shift current realizes a high-speed response of about several picoseconds, which is comparable to that of the band excitation shift current.

[0044] <Example 4: Measurement Results of Phonon Shift Current in Ferroelectric Material BaTiO3> Figure 12 shows the phonon shift current when a bias voltage is applied between electrode 2 and electrode 3 when the electric field component of the incident light of phonon energy is parallel to the polarization direction (100). The bias voltage indicates the voltage applied to electrode 2 with reference to the voltage of electrode 3. When the polarization is positive (in the case of rightward polarization), when the bias voltage is applied from -10V to +10V, the phonon shift current shows a positive current (in the direction flowing from wire 4 to wire 5) of the same magnitude as the zero bias, which is 4μA. Even when the bias voltage is negative, it has a positive value. In the case of negative polarization (in the case of leftward polarization), when the bias voltage is applied from -10V to +10V, the phonon shift current always has a negative value. It is completely different from a resistive element where the flowing current is linearly dependent on the voltage. In contrast, the phonon shift current does not depend on the bias voltage. When polarization exists, the direction of the phonon shift current is uniquely determined by the direction of polarization regardless of the direction of the bias voltage, and a current proportional only to the incident light intensity flows without depending on the bias voltage intensity (see the following paragraph). Even when the bias voltage is zero, a large current is generated between electrode 2 and electrode 3. That is, it shows that by irradiating the photoelectric conversion unit 1 having no p-n junction with light of phonon energy, current can be efficiently extracted from the photoelectric conversion unit 1 through electrodes 2 and 3.

[0045] <Example 5: Measurement Results of Phonon Shift Current in Ferroelectric Material BaTiO3> In FIG. 13, the electric field dependence of the phonon shift current is shown. The phonon shift current shows a quadratic dependence on the electric field. Since the incident light intensity is the square of the electric field, it shows that the phonon shift current is proportional to the incident light intensity. Measuring the phonon shift current shows that the incident light intensity can be measured. The phonon shift current can be used as an optical sensor.

[0046] <Example 6: Measurement Results of Phonon Shift Current in Ferroelectric Material BaTiO3> Figure 14 shows the dependence of the phonon shift current on the azimuth angle (Θ) of the electric field of the incident light when the incident light of the phonon energy is incident perpendicular to the

[0001] plane of BaTiO3. The phonon shift current intensity decreases sinusoidally from the case where the azimuth of the electric field component of the incident light is parallel to the polarization (electric field azimuth angle 0 degrees) to the perpendicular direction (electric field azimuth angle 90 degrees). Furthermore, it increases sinusoidally from the perpendicular direction (electric field azimuth angle 90 degrees) to the parallel direction (electric field azimuth angle 180 degrees) of the incident light. This mechanism will be explained below. Figure 15 shows two types of phonon modes existing in BaTiO3. They are the relaxation mode and the soft mode. The relaxation mode is a mode that oscillates in the positive and negative directions of the polarization direction. It is a mode in which the Ti atom vibrates left and right around the reference point. The soft mode is a mode in which the Ti atom and the oxygen atom vibrate from the reference point in a plane perpendicular to the polarization. The vibration directions of the Ti atom and the oxygen atom vibrate in opposite directions to each other. As shown in Figure 16, the phonon modes of BaTiO3 have large values in the imaginary part ε" of the dielectric constant in the 0 - 20 meV region. The value of the imaginary part ε" of the dielectric constant of the relaxation mode of BaTiO3 is from Non-Patent Document 4 (J. Hlinka, et. al.). It has a larger value as the energy increases from low energy to high energy. The value of the imaginary part of the dielectric constant of the soft mode of BaTiO3 is from Non-Patent Document 5 (T. Hoshina, et. al.). The smaller the energy, the larger the value of the imaginary part ε" of the dielectric constant of the soft mode, and the absorption intensity increases. At 30 cm -1 (0.33 mm, 3.7 meV), the imaginary part of the dielectric constant is 700. Furthermore, it has a value of the huge imaginary part of the dielectric constant ε" even in the lower wave number region. It shows that the phonon modes of BaTiO3 have a large absorption rate in the incident light energy region from 1 meV to 10 meV. The light energy from 1 meV to 10 meV of the incident light shown in Figure 7B can be coupled with these phonon modes.

[0047] Figure 17 shows the experimental arrangement of the electric field orientation and polarization of the incident light and the atomic model of the relaxation mode. The electric field vector E(ω) of the light is in the same direction as the oscillation direction of the relaxation mode. At this arrangement, the electric field vector E(ω) of the incident light couples with the relaxation mode. Figure 18 shows the experimental arrangement of the electric field orientation and polarization of the incident light and the atomic model of the soft mode. The electric field vector E(ω) of the light is in the same direction as the oscillation direction of the soft mode. At this arrangement, the electric field vector E(ω) of the incident light couples with the soft mode. For the phonon shift current to occur, the coupling constant between the phonon and the electron of these modes must be finite. This can be discussed from the group theory of the crystal structure. The phonon-electron coupling constants of the relaxation mode and the soft mode in the BaTiO3 crystal structure are non-zero finite values.

[0048] As described above, the electric field orientation dependence of the incident light of the phonon shift current in Example 6 is such that when the electric field orientation angle is zero (the electric field direction is parallel to the polarization), the phonon shift current due to the relaxation mode flows. As the angle increases, the contribution of the relaxation mode decreases and the contribution of the soft mode increases. At the electric field orientation angle of 90 degrees (the electric field direction is perpendicular to the polarization), the phonon shift current due to the contribution of the soft mode flows. The electric field orientation dependence of the incident light of the phonon shift current can be explained by the contributions of the relaxation mode and the soft mode.

[0049] <Example 7: Measurement Results of Phonon Shift Current in Ferroelectric Material BaTiO3> FIG. 19 shows the temperature dependence of the phonon shift current due to the soft mode (black circles) and the temperature dependence due to the relaxation mode (white circles). In both cases, the phonon shift current occurs from around the Curie temperature of 395°C. When the polarization direction is in the positive direction, the phonon shift current becomes a positive current. When the polarization direction is in the negative direction, the phonon shift current becomes a negative current. The phonon shift current caused by the soft mode has a large value near the transition temperature. Near room temperature, the phonon shift current due to the relaxation mode is somewhat larger than that due to the soft mode. When detecting infrared rays or millimeter waves, the phonon shift current has an incident light with an electric field in all 360 degrees, so a phonon shift current combined with both the relaxation mode and the soft mode phonon modes flows.

[0050] <Practical Example 1: Infrared Sensor, Infrared Image Sensor, Infrared Camera> Practical Example 1 is a practical example of the phonon shift current for an infrared sensor, an infrared image sensor, and an infrared camera.

[0051] As shown in FIG. 20, the infrared sensor 33 includes a photoelectric conversion element 10, a current detection unit 101, and a detection signal display unit 33c. The photoelectric conversion element 10, as described above, receives the infrared rays emitted by the object on the irradiation surface 1a of the photoelectric conversion unit 1 via the filter element 6, and takes out the current generated thereby from the electrodes 2 and 3. The current detection unit 101, as described above, detects the current generated by the photoelectric conversion element 10. Thereby, the intensity of the infrared rays received on the irradiation surface 1a is detected. The detection signal display unit 33c includes a display device that displays the detection result of the current amount by the current detection unit 101, such as the oscilloscope 102 described above.

[0052] FIG. 21 shows the flow of optical detection using the photoelectric conversion method according to an embodiment of the present invention. Here, infrared detection using the infrared sensor 33 will be described as an example.

[0053] First, in step S102, a polling process is executed. When the polar material constituting the photoelectric conversion unit 1 is a ferroelectric material, an electric field is applied to the photoelectric conversion unit 1 in the separation direction of the electrodes 2 and 3 to align the polarization direction of the photoelectric conversion unit 1 in the separation direction. The details of the polling process are as described above. Note that if the polarization direction of the photoelectric conversion unit 1 has already been aligned in the separation direction, step S102 may be omitted.

[0054] Next, in step S104, the irradiation surface 1a of the photoelectric conversion unit 1 formed using a polar material having a crystal structure with broken space inversion symmetry is irradiated with light such as infrared light having an energy smaller than the bandgap of the polar material. The infrared light emitted by the object is received by the irradiation surface 1a of the photoelectric conversion unit 1. The light passes through the filter element 6, so that at least the light component having an energy equal to or greater than the bandgap of the polar material is cut off, and the light component having an energy smaller than that, particularly the light component having an energy corresponding to the phonon energy of the polar material of the photoelectric conversion unit 1, is received by the irradiation surface 1a.

[0055] Next, in step S106, the current generated in the photoelectric conversion unit 1 is extracted from the electrodes 2 and 3 disposed at intervals with the irradiation surface 1a interposed therebetween at the end of the photoelectric conversion unit 1 or on the photoelectric conversion unit 1, and detected by the current detection unit 101. The detection signal is transmitted to the detection signal display unit 33c.

[0056] In step S108, the detection signal display unit 33c displays the detection signal output from the current detection unit 101. Note that the detection result may be stored in a storage device (not shown) or the like. Thus, the flow ends.

[0057] Also, as shown in FIG. 22, the infrared image sensor 34 includes a plurality of photoelectric conversion elements 10 and a plurality of current detection units 101. The plurality of photoelectric conversion elements 10 are arranged in a two-dimensional plane, and the surfaces of the respective photoelectric conversion units (i.e., the irradiation surfaces 1a) are arranged in a two-dimensional plane. The two-dimensional infrared rays are received on the surfaces of the respective photoelectric conversion units of the plurality of photoelectric conversion elements 10, and the currents generated accordingly are taken out from the electrodes 2 and 3 of each photoelectric conversion element 10. The plurality of current detection units 101 detect the currents generated by the plurality of photoelectric conversion elements 10 and output two-dimensional detection signals.

[0058] In the example shown in FIG. 22, the plurality of photoelectric conversion elements 10 (Xm, Yn) (m = 1 to M, n = 1 to N) are arranged in an M-row and N-column matrix, and current detection units 101 (101-1) to (101-M) are provided for each column of the photoelectric conversion elements 10. The M photoelectric conversion elements 10 (X1, Yn) to (XM, Yn) belonging to the first row to the Nth row are sequentially connected to the current detection units 101 (101-1) to (101-M), respectively, and the current amounts are detected.

[0059] Also, as shown in FIG. 23, the infrared camera 35 includes the above-described infrared image sensor 34, a detection signal display unit 35c, and a detection signal storage unit 35d. The detection signal display unit 35c is a display device that displays a two-dimensional image. The detection signal storage unit 35d is a storage device such as a flash memory that stores image data. The infrared camera 35 sequentially extracts a plurality of infrared signals from each of the plurality of photoelectric conversion elements 10 included in the infrared image sensor 34, displays them as a two-dimensional image on the detection signal display unit 35c and / or stores the image data in the detection signal storage unit 35d.

[0060] The flow of image detection using the infrared image sensor 34 or the infrared camera 35 is the same as the flow of infrared detection using the above-described infrared sensor 33, except that the plurality of photoelectric conversion elements 10 operate.

[0061] There are two requirements for the infrared sensor. One is the ability to detect infrared wavelengths radiated by an object having a temperature near 300K, that is, infrared wavelengths from 1μm to 30μm. The second is to have sensitivity to infrared wavelengths in the atmospheric windows (regions with low absorption of water and carbon dioxide). Fig. 24 shows the data of the imaginary part of the dielectric constant ε" of phonons of BaTiO3 in the high energy region (Non-Patent Document 4). The relaxation mode of BaTiO3 is 520cm -1, it has a large value of the imaginary part of the dielectric constant at an energy in the 64 meV region. The energy of this relaxation mode corresponds to a wavelength of 19.2 μm. The energy of this relaxation mode exists within the Q band (17 μm to 25 μm) of the atmospheric window. From the above, the 19.2 μm relaxation mode of BaTiO3 can be used as the detection wavelength of an infrared sensor. Among infrared sensors, the only one that can be used at room temperature is the bolometer. The bolometer uses a thinned VOx or amorphous silicon thin film to increase sensitivity. It is a method of reading minute resistance changes in the thin film due to extremely small temperature changes caused by infrared irradiation. This change rate is extremely small. Therefore, the sensitivity is low. In principle, it utilizes the high-resistance effect caused by thermal disturbance due to infrared heating for resistance changes. The influence of the inhomogeneous component of thermal disturbance caused by heat from sources other than the object to be measured or electron scattering due to material impurities cannot be avoided. Therefore, the influence of ambient temperature disturbance cannot be avoided. The response time depends on the thermal response time, the thermal equilibrium time is long, and the response time cannot be shortened. It is about several tens of milliseconds. For this reason, infrared image sensor images form afterimages. The image resolution is low. There are many factors contributing to variations in sensor sensitivity, such as fluctuations in the infrared-temperature conversion coefficient of the material and variations in specific heat due to material inhomogeneity. Despite these many problems, there is currently no alternative, so it is widely commercialized as an infrared sensor for temperature measurement operating at room temperature, as well as an infrared image sensor and an infrared camera. Currently, the widely used measurement of human body temperature, such as on the forehead, is an example of this application. The fields where it is required are wide, such as in-vehicle cameras, smartphones, and weapon detection. A sensor using a phonon shift current having sensitivity to the 19.2 μm relaxation mode of BaTiO3 can provide an ultra-high-speed, high-sensitivity, thermal-noise-free infrared sensor. Thereby, an infrared image sensor and an infrared camera having ultra-high speed, high sensitivity, thermal-noise-free, high resolution, and high pixel count can be provided. BaTiO3 can be used from near 0 °C to near 120 °C.

[0062] <Practical Example 2: Millimeter-Wave Radar and Two-Dimensional Millimeter-Wave Radar> Practical Example 2 is a practical example of phonon shift current for a millimeter-wave radar and a two-dimensional millimeter-wave radar.

[0063] As shown in FIG. 25, the millimeter-wave radar 31 includes a photoelectric conversion element 10, a current detection unit 101, and a detection signal display unit 31c. As described above, the photoelectric conversion element 10 receives the millimeter wave reflected by the object on the irradiation surface 1a of the photoelectric conversion unit 1 via the filter element 6, and extracts the current generated accordingly from the electrodes 2 and 3. As described above, the current detection unit 101 detects the current generated by the photoelectric conversion element 10. Thereby, the intensity of the millimeter wave received on the irradiation surface 1a is detected. The detection signal display unit 31c includes a display device that displays the detection result of the current amount by the current detection unit 101, such as the above-described oscilloscope 102.

[0064] The flow of millimeter-wave detection using the millimeter-wave radar 31 is the same as the flow of infrared detection using the above-described infrared sensor 33, except that the millimeter wave is emitted from a millimeter-wave transmitter (not shown) toward the object and the millimeter wave reflected from the object is received on the irradiation surface 1a of the photoelectric conversion unit 1.

[0065] An in-vehicle radar that can measure the distance to a target object and the speed of the target object has become an essential technology for vehicle driving automation. The frequency used in in-vehicle radars ranges from 20 GHz (wavelength 15 mm, 0.082 meV) to 100 GHz (wavelength 3 mm, 0.41 meV). The target object is irradiated with FM-modulated millimeter waves. The frequency of the reflected wave from the target object changes according to the distance and speed of the target object. The minute frequency change is measured as the beat frequency (frequency difference) to instantaneously measure the distance to the target object and the speed of the target object. To date, sensors in this frequency band have used waveguides. The inside of the waveguide is air. Since the size of the waveguide sensor uses a millimeter-wave resonator, several centimeters are required. The size of the sensor is large and is too large to be installed in the front part of the vehicle. Also, the resonator sensor has low sensitivity. The product price is also high. Despite these major problems, there has been no alternative millimeter-wave sensor until now. Figure 16 shows that the soft mode of BaTiO3 in the example has a large imaginary part of the dielectric constant even at a small energy of 1 meV or less. Therefore, millimeter-wave light in the 20 GHz to 100 GHz region generates a phonon shift current. A sensor using the phonon shift current can be used as a millimeter-wave radar. Since the optoelectronic conversion element can be made small, the millimeter-wave radar is optimal for in-vehicle use. A phonon shift current sensor using BaTiO3 that is sensitive to millimeter waves from 15 mm to 3 mm is put into practical use as a highly sensitive, ultra-high-speed, thermal-noise-free millimeter-wave radar.

[0066] Furthermore, if the millimeter-wave radar 31 is arranged in a two-dimensional plane, a two-dimensional millimeter-wave radar 32 can be easily realized. As shown in FIG. 26, the two-dimensional millimeter-wave radar 32 includes a plurality of photoelectric conversion elements 10, a plurality of current detection units 101, a detection signal display unit 32c, and a detection signal storage unit 32d. The plurality of photoelectric conversion elements 10 are arranged in a two-dimensional plane, and the surfaces of the respective photoelectric conversion units (i.e., the irradiation surfaces 1a) are arranged in a two-dimensional plane. Millimeter waves are received on the surfaces of the respective photoelectric conversion units of the plurality of photoelectric conversion elements 10, and the currents generated accordingly are taken out from the electrodes 2 and 3 of each photoelectric conversion element 10. The plurality of current detection units 101 detect the currents generated by the plurality of photoelectric conversion elements 10. Thereby, the intensities of the plurality of two-dimensional millimeter waves (i.e., millimeter-wave signals) from the plurality of photoelectric conversion elements 10 are sequentially detected.

[0067] In the example shown in FIG. 26, the plurality of photoelectric conversion elements 10 (Xm, Yn) (m = 1 to M, n = 1 to N) are arranged in an M-row and N-column matrix, and current detection units 101 (101-1) to (101-M) are provided for each column of the photoelectric conversion elements 10. The M photoelectric conversion elements 10 (X1, Yn) to (XM, Yn) belonging to the first row to the Nth row are sequentially connected to the current detection units 101 (101-1) to (101-M), respectively, and the current amounts are detected.

[0068] Furthermore, the detection signal display unit 32c is a display device that displays the millimeter-wave signal. The detection signal storage unit 32d is a storage device such as a flash memory that stores the millimeter-wave signal. The two-dimensional millimeter-wave radar 32 sequentially extracts a plurality of millimeter-wave signals from each of the plurality of photoelectric conversion elements 10, and displays the millimeter-wave signal on the detection signal display unit 32c and / or stores it in the detection signal storage unit 32d.

[0069] The flow of millimeter-wave detection using the two-dimensional millimeter-wave radar 32 is the same as the flow of infrared detection using the aforementioned infrared sensor 33, except that millimeter waves are emitted from a millimeter-wave transmitter (not shown) toward an object, and the millimeter waves reflected from the object are received by the irradiation surface 1a of the photoelectric conversion unit 1 and the plurality of photoelectric conversion elements 10 operate.

[0070] BaTiO₃ can be used from around 0°C to around 120°C. The millimeter-wave radar and the two-dimensional millimeter-wave radar can be used in combination with the infrared camera image. Also, it is compatible with the CMOS process. A millimeter-wave radar-mounted CMOS two-dimensional sensor device can be provided.

[0071] Fig. 27 shows the circuit 20 of an infrared image sensor, an infrared camera, and a two-dimensional millimeter-wave radar composed of a plurality of photoelectric conversion elements. The circuit 20 includes a plurality of photoelectric conversion elements 10, a set of switch elements Tr1, Tr3 connected to the electrode 2 of the plurality of photoelectric conversion elements 10 to select them, a set of switch elements Tr2, Tr4 connected to the electrode 3 of the plurality of photoelectric conversion elements 10 to select them, switch elements T5-1, Tr5-2, T6-1, Tr6-2, Tr7 for controlling voltage application or signal extraction, and selection lines L1, L2 for selecting the photoelectric conversion element 10 (photoelectric conversion section 1).

[0072] Note that the selection line L1 is installed to connect the current generated by the light irradiation received on the irradiation surface 1a to the current detection unit 101. Also, the selection line L2 is used to apply a voltage between the electrodes 2 and 3 of the photoelectric conversion element 10 to align the polarization of the ferroelectric in the electrode directions of the electrodes 2 and 3.

[0073] The plurality of photoelectric conversion elements 10 are arranged in a matrix of, for example, M rows and N columns on one surface to form pixels (Xm, Yn) (m = 1 - M, n = 1 - N). In Fig. 27, as an example, pixels (X1, Y1), (X2, Y1), (X1, Y2), (X2, Y2) composed of four photoelectric conversion elements 10 are shown.

[0074] The switch elements Tr3 and Tr4 are switches for selecting the photoelectric conversion element 10 when a voltage is applied to align the polarization of the ferroelectric in one direction (i.e., when executing the poling process in step S102 in FIG. 21). The switch element Tr3 is provided between the selection line L2 and the electrode 2, and the switch element Tr4 is provided between the selection line L2 and the electrode 3. In the case of the pyroelectric material and the space non-inversion symmetric laminated film, the switch elements Tr3 and Tr4 are not necessary. In the case of the ferroelectric BaTiO3, an electric field of 4 kV / cm is required to align the polarization in the electrode direction as shown in FIG. 3. The voltage between the electrodes may be about 0.4 V if the size of the ferroelectric is 1 μm. The switch elements Tr6-1 and Tr6-2 are switches for turning the poling voltage ON-OFF when poling. By turning ON the switch elements Tr6-1 and Tr6-2, the switch elements Tr3 and Tr4 are turned ON via the selection line L2, and then the switch element Tr7 is turned ON. The poling voltage can be applied to the electrode 2 via the switch element Tr3. The electrode 3 is grounded to the ground via the switch element Tr4. Thereby, the polarization of the photoelectric conversion element 10 can be aligned in the electrode interval direction. This poling process is performed once for the initial set at the time of shipment or when starting the phonon shift current. If deterioration of the ferroelectric polarization occurs, it may be reset as appropriate.

[0075] Note that prior to turning ON the switch element Tr7 and applying the poling voltage to the electrode 2, the switch elements Tr5-1 and Tr5-2 are turned OFF to disconnect the electrodes 2 and 3 from the current detection unit 101. Then, after applying the poling voltage to the electrode 2 for a predetermined time, the switch elements Tr6-1 and Tr6-2 are turned OFF to end the application of the poling voltage, and at the same time, the switch element Tr7 is turned OFF to turn off the poling voltage.

[0076] The switch elements Tr1 and Tr2 are switches for connecting the current generated in the photoelectric conversion material by light irradiation (in the current detection in step S106 of FIG. 21) to flow through the current-voltage conversion element. The switch element Tr1 is provided between the selection line L1 and the electrode 2, and the switch element Tr2 is provided between the selection line L1 and the electrode 3. Turn on the switch elements Tr5-1 and Tr5-2, apply a predetermined voltage to the gates of the switch elements Tr1 and Tr2 via the selection line L1, and turn on the switch elements Tr1 and Tr2. The voltage converted by the current-voltage conversion element 50 is amplified and output externally. A circuit arrangement in which the switch elements Tr1 and Tr2 are installed independently without sharing with the switch elements Tr3 and Tr4 is important. When measuring the phonon shift current, if the switch elements Tr6-1 and Tr6-2 are turned off and the gate voltages of the switch elements Tr3 and Tr4 are floating voltages, the electrode 2 can be circuitously separated from the ground. The electrode can be disconnected from the potential of the substrate (ground) or the like during the measurement of the phonon shift current. For this reason, the influence from the ambient temperature and electromagnetic waves, which are environmental factors of the phonon shift current, becomes an in-phase component. The current-voltage conversion element can be easily configured with a differential CMOS circuit element. Since the differential CMOS circuit element can cancel out the current intensities of the same phase components generated in the photoelectric conversion element 10, the noise resistance characteristics can be dramatically improved. The microbolometer using the thermal-resistance conversion has a reference resistance placed in parallel and is designed to take a resistance difference signal due to thermal fluctuations, but it is insufficient in principle for countermeasures against electrical noise. The microbolometer requires a predetermined standby time for startup. This is also to make the temperature change of the environment other than the measurement object a steady state, but the phonon shift current is not affected by disturbances other than the object. The generation mechanism of the phonon shift current has a characteristic of not responding to thermal noise.

[0077] The pixel (Xm, Yn) can take out the infrared intensity at each pixel as a voltage signal. If Tr5-2 is turned on, (X1, Y1) and (X2, Y1) in the upper row of the photoelectric conversion element array become external signals. If Tr5-1 is turned on, (X1, Y2) and (X2, Y2) in the lower row of the photoelectric conversion element array become external signals. On the display, {(X1,Y1), (X2,Y1), (X3,Y1),,,,,,,,,,,,,,,,,,,,, (XM,Y1)} {(X1,Y2), (X2,Y2), (X3,Y2),,,,,,,,,,,,,,,,,,,,, (XM,Y2)} ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, {(X1,YN), (X2,YN), (X3,YN),,,,,,,,,,,,,,,,,,,,, (XM,YN)} If they are sequentially displayed, they can be displayed as an infrared camera image.

[0078] Assuming that the size of one photoelectric conversion element is 1 μm, the device size is 4 mm, and 1 mm is required for the peripheral circuit, it is easy to have a pixel count of about 2700 * 2700. In contrast, for the pixel count of a microbolometer, in the example where the size of the nanobolometer is 17 μm, 200 * 200 is the limit. The response time of the phonon shift current is in the picosecond to nanosecond level. It is limited by the frequency characteristics of the differential amplifier CMOS transistor. Even if it is about nanoseconds, the pixels can be swept at high speed. It is possible to capture high-speed flying objects. It is possible to detect high-speed jet airplanes, missiles, and rockets. Since the response speed of the bolometer is about several tens of milliseconds, even at the speed of a person walking, afterimages will be generated. High-speed flying objects cannot be detected.

[0079] As described above, the photoelectric conversion element of the present invention can extract current by irradiating light with energy equivalent to the phonon energy existing in the photoelectric conversion element material. The phonon energy existing in the photoelectric conversion element material widely exists in the wavelength range of far-infrared to infrared light from the number 10 GHz band of 15 mm (0.08 meV) to 10 μm (117 meV). Since the phonon shift current does not depend on the mobility of the material from the generation mechanism, it has an ultra-fast response. The phonon shift current is not disturbed by heat and impurity scattering from the generation mechanism. The magnitude of the phonon shift current is about the same as or larger than the magnitude of the band excitation shift current. Therefore, in the millimeter wave to far-infrared region, an epoch-making sensor having ultra-fast response, high sensitivity, and high noise resistance response performance is provided.

[0080] The phonon shift current sensor can be applied to infrared sensors, infrared image sensors, and infrared cameras. The phonon shift current sensor has sensitivity in the range of 3 μm to 30 μm in the wavelength region of room temperature radiation light. BaTiO3 has a phonon energy of 19.2 μm within the Q band region which is the atmospheric window. The phonon shift current sensor can achieve ultra-fast, high-sensitivity, and low-noise specifications at room temperature. The phonon shift current sensor can provide a high-resolution, high-pixel infrared image sensor and an infrared camera that can clearly display a clear high-speed flying object image without afterimages.

[0081] The phonon shift current sensor can be used as a millimeter wave radar. It can detect millimeter waves in the 20 GHz to 100 GHz region required for in-vehicle radars. Since the photoelectric conversion element can be made small, it can be easily placed in the front of the vehicle. The millimeter wave radar is optimal for in-vehicle use. The phonon shift current sensor using BaTiO3 having sensitivity to millimeter waves of 3 mm to 15 mm is provided for practical use as a high-sensitivity, ultra-fast, and thermal noise-free millimeter wave radar. BaTiO3 can be used from room temperature to around 120 °C. The two-dimensional millimeter wave radar can be combined with an infrared camera image. It also has good compatibility with the CMOS process. A CMOS sensor device equipped with a two-dimensional millimeter wave radar can be provided.

[0082] As described above, the present invention has been explained using embodiments. However, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various changes or improvements can be made to the above embodiments. It is clear from the description of the claims that forms with such changes or improvements can also be included in the technical scope of the present invention.

[0083] It should be noted that the execution order of each process such as operations, procedures, steps, and stages in the apparatus, system, program, and method shown in the claims, the specification, and the drawings is not explicitly indicated as "earlier" or "preceding" etc. in particular. Also, unless the output of the previous process is used in the subsequent process, it can be realized in any order. Regarding the operation flow in the claims, the specification, and the drawings, even if it is described using "first," "next," etc. for convenience, it does not mean that it must be implemented in this order.

Explanation of Reference Numerals

[0084] 1... Photoelectric conversion unit, 1a... Irradiation surface, 2, 3... Electrodes, 4, 5... Metal wires, 6... Filter element, 10... Photoelectric conversion element, 20... Circuit, 31... Millimeter-wave radar, 31c... Detection signal display unit, 32... Two-dimensional millimeter-wave radar, 32c... Detection signal display unit, 32d... Detection signal storage unit, 33... Infrared sensor, 33c... Detection signal display unit, 34... Infrared image sensor, 35... Infrared camera, 35c... Detection signal display unit, 35d... Detection signal storage unit, 50... Current-voltage conversion element, 101... Current detection unit, 102... Oscilloscope, L1, L2... Selection lines, Tr1, Tr2, Tr3, Tr4, Tr5-1, Tr5-2, Tr6-1, Tr6-2, Tr7... Switch elements.

Claims

1. A photoelectric conversion unit formed to include an irradiation surface that receives incident light having an energy smaller than the bandgap of a polar material, using a polar material having a crystal structure with broken space inversion symmetry; First and second electrodes disposed at an end of the photoelectric conversion unit or with an interval therebetween across the irradiation surface on the photoelectric conversion unit; A filter element disposed on the optical axis of the incident light and cutting the incident light having an energy of at least the bandgap of the polar material; A photoelectric conversion element comprising the above.

2. The photoelectric conversion element according to claim 1, wherein the irradiation surface receives incident light having an energy corresponding to the phonon energy of the polar material of the photoelectric conversion unit.

3. The photoelectric conversion element according to claim 1 or 2, wherein the polar material is a pyroelectric material or a ferroelectric material.

4. The pyroelectric material is GaFeO 3 , CdS, GaN, ZnO, CdTe, BiTeI, or BiTeBr, and the photoelectric conversion element according to claim 3.

5. The ferroelectric material is BaTiO 3 , SbSI, BiSI, TTF-CA (tetrathiafulvalene-p-chloranil), TTF-BA (tetrathiafulvalene-bromanil), BiFeO 3 , TMB-TCNQ (tetramethylbenzidine-tetracyano quinodimethane), GeTe, CH 3 NH 3 PbI 3 , (2-(ammoniomethyl)pyridinium)SbI 5 , Sn 2 P 2 S 6 , PbTiO 3 , Pb 5 Ge 3 O 11 , PZT (lead zirconate titanate), LiNbO 3 , LiTaO 3 , KNbO 3 , or the photoelectric conversion element according to claim 3, which is KDP (Potassium Dihydrogen Phosphate).

6. The ferroelectric material is BaTiO 3 and The photoelectric conversion element according to claim 5, wherein the irradiation surface receives incident light having a wavelength of 3 mm to 15 mm or a wavelength of 17 μm to 22 μm.

7. The photoelectric conversion unit is a laminated thin film in which an A layer, a B layer, and a C layer having different crystal materials are laminated in the order of ABC from the lower layer, or The laminated thin film is formed by laminating the ABC layers N times (N is an integer of 1 or more) from the lower layer, The photoelectric conversion element according to claim 1 or 2, wherein each of the A layer, the B layer, and the C layer is a thin film composed of atomic layers having a nano-order thickness.

8. The combination of the crystalline materials of the A layer, B layer, and C layer is LaAlO 3 , LaFeO 3 , and LaCrO 3 , or a combination of CaTiO 3 , SrTiO 3 , and BaTiO 3 . The photoelectric conversion element according to claim 7.

9. The photoelectric conversion element according to any one of claims 1 to 8, further comprising at least one of a set of a first switch element and a third switch element for selecting the first electrode and a set of a second switch element and a fourth switch element for selecting the second electrode.

10. The photoelectric conversion element according to claim 9, comprising a first selection line for selecting the photoelectric conversion unit, wherein the first switch element is provided between the first selection line and the first electrode, and the second switch element is provided between the first selection line and the second electrode.

11. The photoelectric conversion element according to claim 10, wherein the first selection line is installed to connect a current generated by the incident light received at the irradiation surface to a current-voltage conversion element.

12. A second selection line for selecting the photoelectric conversion unit is provided, the third switch element is provided between the second selection line and the first electrode, and the fourth switch element is provided between the second selection line and the second electrode. The photoelectric conversion element according to any one of claims 9 to 11.

13. The second selection line is installed for applying a voltage between the first electrode and the second electrode to align the polarization direction of the photoelectric conversion unit in the directions of the first electrode and the second electrode. The photoelectric conversion element according to claim 12.

14. An infrared sensor that includes the photoelectric conversion element according to any one of claims 1 to 13 and detects the intensity of infrared rays received on the irradiation surface by currents taken out from the first and second electrodes.

15. A plurality of the photoelectric conversion elements according to any one of claims 1 to 13 are provided, the plurality of photoelectric conversion elements are arranged in a two-dimensional plane, the surfaces of the photoelectric conversion units of the photoelectric conversion elements are arranged in a two-dimensional plane, and infrared rays are received on the surfaces of the photoelectric conversion units of the plurality of photoelectric conversion elements. An infrared image sensor that outputs a plurality of two-dimensional infrared ray signals from the plurality of photoelectric conversion elements.

16. An infrared camera that includes the infrared image sensor according to claim 15, sequentially extracts a plurality of infrared signals from the infrared image sensor, and displays them as a two-dimensional image.

17. A millimeter wave radar that includes the photoelectric conversion element according to any one of claims 1 to 13 and detects the intensity of millimeter waves received on the irradiation surface by currents taken out from the first and second electrodes.

18. A plurality of the photoelectric conversion elements according to any one of claims 1 to 13 are provided, the plurality of photoelectric conversion elements are arranged in a two-dimensional plane, the surfaces of the photoelectric conversion units of the photoelectric conversion elements are arranged in a two-dimensional plane, and millimeter waves are received on the surfaces of the photoelectric conversion units of the plurality of photoelectric conversion elements. A millimeter wave two-dimensional radar that outputs a plurality of two-dimensional millimeter wave signals from the plurality of photoelectric conversion elements.

19. Irradiating incident light having an energy smaller than the bandgap of the polar material through a filter element that cuts off incident light having an energy of at least the bandgap of the polar material on the irradiation surface of the photoelectric conversion unit formed using a polar material having a crystal structure with broken space inversion symmetry. A step of extracting the current generated in the photoelectric conversion unit from the first and second electrodes disposed at an interval with the irradiation surface interposed therebetween at an end of the photoelectric conversion unit or on the photoelectric conversion unit; A photoelectric conversion method comprising the above.

20. The polar material is a ferroelectric material, The photoelectric conversion method according to claim 19, further comprising a step of aligning the polarization direction of the photoelectric conversion unit in the separation direction by applying an electric field to the photoelectric conversion unit in the separation direction of the first and second electrodes.

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