JP4839977B2 - Infrared sensor device - Google Patents

Description

  The present invention relates to an infrared sensor device.

  Conventionally, as an example of an infrared sensor device, a thermal infrared image sensor having a configuration shown in FIG. 8 has been proposed (see Patent Document 1).

  The thermal infrared image sensor having the configuration shown in FIG. 8 is an infrared sensor in which a plurality of pixels 100 each having a thermal infrared detection element (thermal element) 101 that outputs an analog current value corresponding to a temperature rise are arranged in a matrix. IS ′ and a plurality of pixels 100 in each column of the infrared sensor IS ′ are commonly connected to each column, and a plurality of pixels 100 in each row of the infrared sensor IS ′ are commonly connected to each row. A plurality of clock lines 103, a plurality of buffer amplifiers 107 provided for each vertical readout line 102 to amplify the output of the thermal infrared detecting element 101, and a plurality of integrations for integrating the outputs of the buffer amplifiers 107 for a predetermined time. Circuit 110 and a plurality of storage capacitors CT provided on the subsequent stage side of each integration circuit 110, and each storage capacitor CT And it is capable of reading a time series a voltage from the output terminal VO.

  Here, the thermal-type infrared detection element 101 is configured by a resistance bolometer-type infrared detection element (for example, see Patent Documents 2 and 3). The integration circuit 110 includes an amplifier 110a, an integration capacitor CS connected between the input terminal and the output terminal of the amplifier 110a, and a reset MOS transistor in which a source and a drain are connected between both ends of the integration capacitor CS. It is composed of QS.

  The thermal infrared image sensor disclosed in Patent Document 1 is also provided with offset compensation means for compensating for the offset of the buffer amplifier 107.

In addition to the resistance bolometer-type infrared detection element, a dielectric bolometer-type infrared detection element, a thermopile-type infrared detection element (see Patent Document 3), and the like are widely used as the thermal infrared detection element. Yes.
Japanese Patent Laid-Open No. 10-145679 JP 2000-97765 A Japanese Patent No. 3040356

  By the way, the frequency of the signal component of the output of the infrared sensor IS ′ is about 0 to several tens Hz, and the output fluctuation when the amount of the incident infrared ray fluctuates due to the movement of the person is very small. In the infrared sensor device, when the output of the infrared sensor IS ′ is integrated and amplified by the integration circuit 110, flicker noise is generated in the same low frequency band as the signal component, and is affected by flicker noise and white noise (white noise). S / N ratio will fall.

  This invention is made | formed in view of the said reason, The objective is to provide the infrared sensor apparatus which can improve S / N ratio.

According to the first aspect of the present invention, an infrared sensor that generates an analog output value corresponding to a temperature change due to infrared absorption, and the output of the infrared sensor is modulated with a modulation signal having a frequency sufficiently higher than the frequency of the signal component. A modulator, an amplifier for amplifying the output of the modulator, a demodulator for extracting the output of the amplifier with a demodulated signal synchronized with the modulated signal, and a cutoff frequency provided at a subsequent stage of the demodulator from the frequency of the demodulated signal An analog low-pass filter that is lower and higher than the frequency range of the signal component of the infrared sensor, and an A / D converter that analog-digital converts the output of the analog low-pass filter at a sufficiently high sampling frequency with respect to the frequency of the signal component of the infrared sensor; The cutoff frequency provided at the rear stage of the A / D converter is higher than the frequency range of the signal component of the infrared sensor. It and a digital low-pass filter is less than half the sampling frequency of the converter, the infrared sensor is an array sensor having a plurality of thermal type infrared sensing device, modulator the output of each thermal type infrared sensing device A scanner for generating a scanning signal to be input in time series, and a signal separator which is inserted between the amplifier and the demodulator and separates the output of the amplifier into an output corresponding to each thermal infrared detection element, and and characterized in that it comprises a.

  According to the present invention, the modulator that modulates the output of the infrared sensor with a modulation signal having a frequency sufficiently higher than the frequency of the signal component, the amplifier that amplifies the output of the modulator, and the output of the amplifier as the modulation signal. Since it is equipped with a demodulator that extracts with a synchronized demodulated signal, it can separate the signal component of the infrared sensor and the flicker noise generated by the amplifier while amplifying the minute output of the infrared sensor, Flicker noise can be removed by an analog low-pass filter that is provided and has a cutoff frequency lower than the frequency of the demodulated signal and higher than the frequency range of the signal component of the infrared sensor, and sampling that is sufficiently higher than the frequency of the signal component of the infrared sensor A / D converter for analog-digital conversion of analog low-pass filter output by frequency, and A / D converter A digital low-pass filter that is provided on the rear stage side and has a cutoff frequency higher than the frequency range of the signal component of the infrared sensor and less than half of the sampling frequency of the A / D converter. Since white noise can be reduced by the low-pass filter, flicker noise and white noise can be reduced, and the S / N ratio can be improved.

Further, according to this invention, a scanner for generating a scanning signal for time-sequentially receiving the output of the thermal type infrared sensing device of the infrared sensor to modulator, demodulation unit and the amplifier since the output of the inserted amplifier and a signal separator for separating the output corresponding to each of the thermal-type infrared detection element between, the one output of the plurality of thermal type infrared sensing device As compared with the case where the output of each thermal infrared detection element is amplified by a different amplifier, variation in the S / N ratio can be reduced, and the circuit configuration can be simplified and the cost can be reduced.

According to a second aspect of the present invention, in the first aspect of the invention, the thermal infrared detection element is a resistance bolometer type infrared detection element, and the scanning signal of the scanner and the modulation signal of the modulator are synchronized. Features.

  According to the present invention, the timing condition for modulating the output of each thermal infrared detection element by the modulator can be made constant, and the performance can be stabilized.

  According to the first aspect of the present invention, flicker noise and white noise can be reduced, and the S / N ratio can be improved.

(Embodiment 1)
As shown in FIG. 1, the infrared sensor device of the present embodiment includes an infrared sensor IS that generates an analog output value corresponding to a temperature change due to infrared absorption, and an output of the infrared sensor IS that has a frequency (0 A modulator 3 that modulates with a modulation pulse of a sufficiently high frequency (the frequency at which the amplitude level of flicker noise is sufficiently lower than the amplitude level of the signal component, for example, 30 kHz), An amplifier 4 for amplifying the output of the modulator 3, a demodulator 6 for extracting the output of the amplifier 4 with a demodulated pulse synchronized with the modulation pulse, and a cutoff frequency provided at the subsequent stage of the demodulator 6 is the frequency of the demodulated pulse. (For example, the frequency when the demodulation pulse period is determined as [modulation pulse period] × [number of signals separated by the signal separator 5 described later] If the frequency of the pulse is 30 kHz and the number of signals separated by the signal separator 5 is 3, an analog low-pass filter (analog low) that is lower than 10 kHz and higher than the frequency range (0 to 10 Hz) of the signal component of the infrared sensor IS. Band-pass filter) 7, an A / D converter 8 for analog-to-digital conversion of the output of the analog low-pass filter 7 at a sufficiently high sampling frequency (for example, 10 kHz) with respect to the frequency of the signal component of the infrared sensor IS, and A / D A digital low-pass filter (digital) that is provided on the rear stage side of the converter 8 and whose cutoff frequency is higher than the frequency range of the signal component of the infrared sensor IS and is half or less (for example, 20 Hz) of the sampling frequency of the A / D converter 8. Low-pass filter) 9. In the present embodiment, the modulation pulse constitutes a modulation signal, and the demodulation pulse constitutes a demodulation signal.

  In this embodiment, the cutoff frequency of the analog low-pass filter 7 is set to 5 kHz, the sampling frequency of the A / D converter 8 is set to 10 kHz, and the cutoff frequency of the digital low-pass filter 9 is set to 20 Hz. These numbers are examples. However, from the sampling theorem, it is desirable that the sampling frequency of the A / D converter 8 is at least twice the cutoff frequency of the analog low-pass filter 7. The output of the infrared sensor IS includes a frequency component of about 10 Hz when the amount of incident infrared rays varies due to the movement of a person, but the direct current when there is no change in the amount of incident infrared rays when the person is stationary. It becomes.

  Further, the infrared sensor device of the present embodiment is an array sensor in which a plurality of infrared sensors IS (three in the present embodiment) are arranged in the form of an array of thermal infrared detection elements 1 (see FIG. 2). Each of the demodulator 6 and the analog low-pass filter 7 is provided in plural (three in this embodiment), and the output of each thermal infrared detecting element 1 is input to the modulator 3 in time series. A scanner 2 that generates a scanning signal, and a signal separator that is inserted between the amplifier 4 and the plurality of demodulators 6 and separates the output of the amplifier 4 into outputs (signals) corresponding to the thermal infrared detection elements 1 respectively. 5 and a multiplexer 10 that is inserted between the plurality of analog low-pass filters 7 and the A / D converter 8 and alternatively inputs the outputs of the plurality of analog low-pass filters 7 to the A / D converter 8. Eteiru.

  Here, in the present embodiment, a controller that provides a timing signal for synchronizing the scanning signal of the scanner 2, the modulation pulse of the modulator 3, and the signal separator 5 to the scanner 2, the modulator 3, and the signal separator 5. (Not shown). Here, in this embodiment, the switching frequency of the thermal infrared detection element 1 that is cyclically selected by the scanning signal of the scanner 2 is the same as the frequency of the modulation pulse of the modulator 3 (modulation frequency). It may be lower than the frequency. However, the infrared sensor device can be simplified by synchronizing the modulation pulse and the timing signal. The signal separator 5 includes a plurality (three in this embodiment) of switch elements (not shown) for separating the output of the amplifier 4 into outputs corresponding to the respective thermal infrared detection elements 1. Each switch element is cyclically turned on by a timing signal provided from the controller.

  In the present embodiment, the plurality of thermal infrared detection elements 1 are arranged in a one-dimensional array, but may be arranged in a two-dimensional array (matrix). In this case, horizontal scanning is performed. And a scanning device for vertical scanning (vertical scanning circuit), each scanning is performed so that the output of each thermal infrared detection element 1 is input to the modulator 3 in time series. A scanning signal may be generated from the detector, and an infrared image having each thermal infrared detection element 1 as a pixel can be obtained.

As shown in FIGS. 2A and 2B, the thermal infrared detecting element 1 is disposed on the base substrate 11 and one surface side of the base substrate 11 (upper surface side in FIG. 2B) and absorbs infrared rays. temperature detector 13 and the temperature detection unit 13 is temperature detection unit 13 so as to be spaced apart from the one surface of the base plate 11 (upper surface in FIG. 1 (b)) for detecting a temperature change due to the absorption while A heat insulating portion 14 that thermally insulates the temperature detecting portion 13 and the base substrate 11, an infrared absorbing layer 15 that is laminated on the opposite side of the temperature detecting portion 13 from the base substrate 11 side, and absorbs infrared rays, and a base substrate 11 and an infrared reflecting film 16 that reflects infrared rays formed on the one surface and transmitted through the infrared absorption layer 15, the temperature detection unit 13, and the heat insulation unit 14 toward the temperature detection unit 13. In the present embodiment, the infrared sensor IS includes a plurality of thermal infrared detection elements 1, but a plurality of temperature detection units 13 are arranged in an array on the one surface side of one base substrate 11, Each temperature detection unit 13 is supported by a separate heat insulation unit 14 and thermally insulated from the base substrate 11.

Here, the base substrate 11 includes a silicon substrate 11a and an insulating film 11b made of a silicon oxide film formed on one surface side of the silicon substrate 11a. Note that the thermal infrared detection element 1 in the present embodiment assumes infrared in the wavelength band of 8 μm to 13 μm emitted from the human body as infrared to be detected, and employs SiON as the material of the infrared absorption layer 15. As a material of the infrared reflecting film 16, Al-Si is adopted. The material of the infrared absorption layer 15 is not limited to SiON, and for example, Si ₃ N ₄ , SiO ₂ , gold black, or the like may be employed.

  Further, if the center wavelength of the infrared ray to be detected is λ [μm] and the distance between the infrared absorbing layer 15 and the infrared reflecting film 16 is d [μm], d = λ / 4 is designed. Since infrared rays are emitted from the human body, λ = 10 μm and d = 2.5 μm are designed. Therefore, in the thermal infrared detection element 1 in the present embodiment, a part of the infrared light incident on the infrared absorption layer 15 is absorbed by the infrared absorption layer 15 and the temperature detection unit 13 and the rest is transmitted but reflected by the infrared reflection film 16. Then, it returns to the infrared absorption layer 15 again, and since the distance d between the infrared absorption layer 15 and the infrared reflection film 16 is λ / 4, it resonates with the wavelength of the infrared ray to be detected and the absorption efficiency increases. In short, in the present embodiment, the infrared absorbing layer 15 and the infrared reflecting film 16 constitute a resonator that resonates with the wavelength of the infrared rays to be detected and makes the infrared rays remain.

  The heat insulating part 14 is arranged so as to be separated from the one surface of the base substrate 11 and the temperature detecting part 13 is formed on the side opposite to the base substrate 11 side, and the support part 41 and the base substrate 11 are connected to each other. The two leg portions 42 and 42 are provided.

  On the other hand, the above-described temperature detection unit 13 includes a metal film (for example, Al) on the one surface of the base substrate 11 via the wirings 18a and 18c formed along the leg portions 42 and 42 of the heat insulating unit 14. -Electrically connected to the conductor patterns 12a, 12c made of a Si film or the like. In the infrared sensor IS according to the present embodiment, as described above, a plurality of temperature detectors 13 are arranged on the one surface side of one base substrate 11, and two conductor patterns 12a and 12c forming a pair are provided. Since the one surface side of the base substrate 11 is electrically connected to different bus wirings, the outputs of the temperature detection units 13 can be taken out to the outside separately.

  The thermal infrared detection element 1 in this embodiment is a resistance bolometer type infrared detection element, and the temperature detection unit 13 is formed on a lower electrode 13a made of a chromium film formed on a support unit 41, and on the lower electrode 13a. The thermistor includes a resistor layer 13b made of an amorphous silicon film and an upper electrode 13c made of a chromium film formed on the resistor layer 13b. In the present embodiment, amorphous silicon is used as the material of the resistor layer 13b. However, the material of the resistor layer 13b is not limited to amorphous silicon, and for example, titanium, vanadium oxide, or the like may be used.

  Here, in the temperature detection unit 13, the lower electrode 13 a is electrically connected to one conductor pattern 12 a via a wiring 18 a formed along one leg 42, and the upper electrode 13 c is connected to the other leg 42. Is electrically connected to the other conductor pattern 12c through a wiring 18c formed along the line 18c. In this embodiment, the same chromium as that of the lower electrode 13a is used as the material of the one wiring 18a, and the same chromium as that of the upper electrode 13c is used as the material of the other wiring 18c. The temperature detector 13 can be formed using a general thin film forming technique by appropriately selecting a material.

By the way, in the thermal infrared detecting element 1, the leg portions 42, 42 of the above-described heat insulating portion 14 are cylindrical support post portions 42a in which the one surface side of the base substrate 1 is erected on the conductor patterns 12a, 12c. , 42a, and beam portions 42b, 42b connecting the upper end portions of the support post portions 42a, 42a and the support portion 41, and a gap 17 is formed between the support portion 41 and the base substrate 11. Yes. Here, each beam part 42b and 42b is formed in the L-shaped planar shape, and is arrange | positioned so that it may have rotational symmetry with respect to the central axis along the thickness direction of the support part 41. As shown in FIG. Note that the line widths of the portions formed along the beam portions 42b and 42b of the leg portions 42 and 42 in the wirings 18a and 18c described above are beam portions in order to suppress heat transfer through the wires 18a and 18c. It is set sufficiently smaller than the width dimension of 42b, 42b. Moreover, the site | part formed along support post part 42a, 42a among wiring 18a, 18c is formed ranging over the whole inner peripheral surface of support post part 42a, 42a, and the surface of conductor pattern 12a, 12c. The support post portions 42a and 42a are reinforced by the wirings 18a and 18c.

  Further, in the thermal infrared detecting element 1, the leg portions 42 and 42 and the support portion 41 of the heat insulating portion 14 are formed of a porous material. Here, porous silica, which is a kind of porous silicon oxide, is adopted as the porous material of the legs 42, 42 of the heat insulating part 14 and the support part 41, but a kind of porous silicon oxide organic polymer. Methyl-containing polysiloxane, Si-H-containing polysiloxane which is a kind of porous silicon oxide-based inorganic polymer, silica aerogel, etc. may be employed. As the porous material, porous silicon oxide, If a material selected from the group consisting of a silicon oxide organic polymer and a porous silicon oxide inorganic polymer is employed, the heat insulation can be improved as compared with the case where nonporous silicon oxide is employed as the heat insulating portion 4.

  Here, the heat insulating portion 14 in the present embodiment is constituted by a porous silica film (porous silicon oxide film) having a porosity of 60%. However, if the porosity is too small, a sufficient heat insulating effect cannot be obtained and the porous section is porous. If the degree is too high, the mechanical strength becomes weak and it becomes difficult to form a structure. Therefore, the porosity of the porous silica film is preferably set appropriately within a range of about 40% to 80%, for example.

Here, the total thermal conductance G of the two leg portions 42 and 42 is such that the thermal conductivity of the material of the leg portion 42 is α [W / (m · K)], the length of the leg portion 42 is L [μm], If the cross-sectional area of the cross section perpendicular to the extending direction of the leg portion 42 is S, it is obtained by G = 2 × α × (S / L). However, if the material of the leg portion 42 is SiO ₂ , If α = 1.4 [W / (m · K)], L = 50 [μm], S = 10 [μm ² ], the thermal conductance G is
G = 2 × α × (S / L) = 560 × 10 ⁻⁹ [W / K].

On the other hand, when the leg portion 42 is composed of a porous silica film having a porosity of 60% as in this embodiment, α = 0.05 [W / (m · K)], L = 50 [μm] and S = 10 [μm ² ], the thermal conductance G is
G = 2 × α × (S / L) = 2.0 × 10 ⁻⁸ [W / K]
Thus, the thermal conductance G can be set to a value smaller than one tenth of the thermal conductance G of the comparative example in which the leg portion 42 is formed of a silicon oxide film, and the heat transfer through the leg portions 42 and 42 can be further improved. It can be suppressed and high sensitivity can be achieved.

In addition, the heat capacity C of the support part 41 is such that the volume specific heat of the support part 41 is c _v , the cross-sectional area orthogonal to the thickness direction of the support part 41 is A [μm ² ], and the thickness of the support part 41 is d [μm]. Then, C = c _v × A × d. Here, if the material of the support portion 41 is SiO ₂ , c _v = 1.8 × 10 ⁶ [J / (m ³ · K)], A = 2500 [μm ² ], d = 0. If 5 [μm], the heat capacity C of the support portion 41 is
C = c _v × A × d = 22.6 × 10 ⁻¹⁰ [J / K].

On the other hand, when the support portion 41 is composed of a porous silica film having a porosity of 60% as in this embodiment, c _v = 0.88 × 10 ⁶ [J / (m ³ · K)], A = 2500 [μm ² ], and d = 0.5 [μm], the heat capacity C of the support 41 is
C = c _v × A × d = 11.0 × 10 ⁻¹⁰ [J / K]
Thus, the heat capacity C of the support portion 41 can be set to a value smaller than half that of the comparative example in which the support portion 41 is made of a silicon oxide film, and the time constant is reduced to increase the response speed. I can plan.

  Hereinafter, an operation example of the infrared sensor device of the present embodiment will be described with reference to FIGS. 3 and 4.

  For example, if the output waveforms of the three thermal infrared detection elements 1 of the infrared sensor IS are “a”, “b”, and “c” in FIG. 3A, the output of each thermal infrared detection element 1 is The frequency spectrum distribution (power density spectrum distribution) is “a”, “b”, and “c” in FIG. 4A, and the frequency spectrum distribution of white noise is “d” in FIG. 4A.

  Here, assuming that the modulation pulse of the modulator 3 has a waveform as shown in FIG. 3B and the modulation frequency is fc (the period of the modulation pulse is 1 / fc), the output of the modulator 3 is amplified. The output waveform of the amplifier 4 is as shown in FIG. Here, the frequency spectrum distribution of the output of the infrared sensor IS input to the modulator 3 is the same as that of FIG. 4A as shown in FIG. 4B, and the frequency spectrum distribution of the output after the modulation by the modulator 3 is performed. Is as shown in FIG. That is, the output of the thermal infrared detection element 1 is converted into an alternating current at the modulation frequency fc, and the signal components “I”, “B”, and “C” of each thermal infrared detection element 1 shift to the modulation frequency fc. In FIG. 4C, “i”, “b”, and “c” indicate signal components, “d” indicates white noise, and “e” indicates flicker noise.

  Next, the output waveforms (that is, the input waveform of each demodulator 6) corresponding to each thermal infrared detecting element 1 output from the signal separator 5 following the amplifier 4 are shown in FIG. 3 (d-1). Waveforms such as “A”, “B” in FIG. 3D-2, and “C” in FIG. 3D-3, and the frequency spectrum distribution are shown in FIG. 4D-1 and FIG. -2) and FIG. 4 (d-3). 4D-1 to 4D-3, “I”, “B”, and “C” indicate signal components, “D” indicates white noise, and “E” indicates flicker noise.

  Next, output waveforms corresponding to the thermal infrared detection elements 1 output from the analog low-pass filters 7 after being demodulated by the demodulator 6 are shown in FIGS. 3 (e-1) and 3 (e), respectively. -2) and the waveform as shown in FIG. 3 (e-3), and the frequency spectrum distribution is as shown in FIG. 4 (e-1), FIG. 4 (e-2), and FIG. 4 (e-3). Here, the demodulated pulse of the demodulator 6 has the same pulse width as that of the modulated pulse and the period is tripled, so that the low-frequency generated by the thermal infrared detecting element 1 and the amplifier 4 by passing through the demodulator 6 is reduced. The flicker noise in the frequency band moves to the frequency (fc / 3) of the demodulated pulse, and the signal component of the thermal infrared detecting element 1 moves to the original low frequency band. 4 (e-1), FIG. 4 (e-2), and FIG. 4 (e-3) show the frequency of the signal component of the thermal infrared detection element 1 whose cutoff frequency is lower than the frequency of the demodulation pulse. Since the frequency spectrum distribution corresponds to the output waveform output from the analog low-pass filter 7 higher than the frequency band, the frequency spectrum distribution cut by the analog low-pass filter 7 is indicated by a broken line. 4 (e-1) to (e-3), “i”, “b”, “ha” indicate signal components, “d” indicates white noise, and “e” indicates flicker noise. As shown by the broken line, part of the white noise “d” and flicker noise “e” are removed by the analog low-pass filter 7.

  Next, each thermal infrared detection element 1 output from the A / D converter 8 that performs oversampling of the output of each analog low-pass filter 7 at a sampling frequency sufficiently higher than the frequency of the signal component of the infrared sensor IS is supported. 3 (f-1), FIG. 3 (f-2), and FIG. 3 (f-3), and the frequency spectrum is shown in FIG. 4 (f-1) and FIG. 4 (f-2). ) And FIG. 4 (f-3). 4 (f-1) to (f-3), “i”, “b”, and “c” indicate signal components, and “d” indicates white noise.

  Next, it is output from the digital low-pass filter 9 whose cutoff frequency is higher than the frequency (about 10 Hz) of the signal component of the thermal infrared detecting element 1 and not more than half of the sampling frequency fs of the A / D converter 8. The outputs corresponding to the thermal infrared detection elements 1 are as shown in FIG. 3 (g-1), FIG. 3 (g-2), and FIG. 3 (g-3), respectively, and the frequency spectrum distribution is shown in FIG. g-1), FIG. 4G-2, and FIG. 4G-3. 4 (g-1) to (g-3), “i”, “b”, “ha” indicate signal components, and “d” indicates white noise. FIG. 4 (f-1) The white noise “d” is reduced compared to (f-3).

In order to simplify the description of the operation example of the infrared sensor device described above, when attention is paid to the output of one thermal infrared detection element 1, the frequency of the output of the thermal infrared detection element 1 input to the modulator 3 The spectrum distribution is as shown in FIG. 5A, and the signal component “I” and the white noise “D” are mixed. Then, after more modulator to modulator 3 to amplify by the amplifier 4, the frequency spectrum distribution is as shown in FIG. 5 (b), signal components "b" and white noise "two" to the amplifier 4 The flicker noise “e” generated in this way is mixed, but the signal component “a” and the flicker noise “e” generated in the amplifier 4 can be separated. Thereafter, as shown in FIG. 5C, the output demodulated by the demodulator 6 shifts the signal component “A” to the original frequency range, while the flicker noise “E” is the frequency of the demodulated pulse (fc / 3). The flicker noise “e” is removed by the analog low-pass filter 7 to obtain a frequency spectrum distribution as shown in FIG. Next, the oversampling is performed by the A / D converter 8 so that the white noise “d” becomes a Nyquist frequency (twice the frequency of the signal component of the thermal infrared detection element 1 as shown in FIG. 6B). Compared to FIG. 6A which is a comparative example when sampling is performed at fs / 2), the power density is low and the frequency spectrum distribution exists up to the high frequency region. Thereafter, the white noise “d” is reduced by passing through the digital low-pass filter 9 having a sharper cutoff characteristic than the analog low-pass filter, and the S / N ratio is improved. In FIGS. 6A to 6C, the white noise amount is AW and the white noise amount AW is indicated by a hatched portion, but the quantization noise in the A / D converter 8 is constant. 6 (a) and FIG. 6 (b) have the same hatched area (n in FIG. 6 (b) is an integer of 2 or more).

  In the infrared sensor device of the present embodiment described above, the modulator 3 that modulates the output of the infrared sensor IS with a modulation pulse having a frequency sufficiently higher than the frequency of the signal component, and the amplifier 4 that amplifies the output of the modulator 3. And the demodulator 5 for extracting the output of the amplifier 4 with a demodulated pulse synchronized with the modulation pulse, the signal component of the infrared sensor IS and the amplifier 4 are amplified while amplifying the minute output of the infrared sensor IS. The generated flicker noise can be separated, and the flicker noise is provided by the analog low-pass filter 7 which is provided at the subsequent stage of the demodulator 6 and whose cutoff frequency is lower than the frequency of the demodulated pulse and higher than the frequency range of the signal component of the infrared sensor IS. An analog low-pass filter that can be removed and that has a sampling frequency sufficiently higher than the frequency of the signal component of the infrared sensor IS A / D converter 8 for analog-to-digital conversion of the output of the A / D converter, and a sampling frequency of the A / D converter 8 provided on the rear stage side of the A / D converter 8 with a cutoff frequency higher than the frequency range of the signal component of the infrared sensor IS Because the digital low-pass filter 9 can reduce the white noise, the flicker noise and the white noise can be reduced, and the S / N ratio is improved. be able to.

  In addition, since the infrared sensor device of the present embodiment includes the signal separator 5 described above, the outputs of the plurality of thermal infrared detection elements 1 of the infrared sensor IS can be amplified by a single amplifier 4. Compared with the case where the output of each thermal infrared detecting element 1 is amplified by a different amplifier, the S / N ratio variation can be reduced, and the circuit configuration can be simplified and the cost can be reduced. Further, in the infrared sensor device of the present embodiment, the thermal infrared detection element 1 is a resistance bolometer type infrared detection element, and the scanning signal of the scanner 2 and the modulation pulse of the modulator 3 are determined by the timing signal from the controller. Since they are synchronized, the condition of timing for modulating the output of each thermal infrared detecting element 1 by the modulator 3 can be made constant, and the performance can be stabilized. The number of the thermal infrared detection elements 1 in the infrared sensor IS is not limited to a plurality, and may be one. When there is only one thermal infrared detection element 1, the above-described scanner 2 and signal separator 5 are It becomes unnecessary.

Moreover, in this embodiment, since the temperature detection part 13 of the thermal type infrared detection element 1 is thermally insulated from the base substrate 11 by the heat insulating part 14 and the heat insulating part 14 is formed of a porous material, the heat insulating part 14 is made of SiO. ₂ and Si ₃ N ₄ , there is an advantage in that the heat insulation is improved and the sensitivity is increased, resulting in an improvement in the S / N ratio. The heat capacity of the section 14 can be reduced, and the response speed can be increased. Moreover, since the heat capacity of the support part 41 can be reduced as compared with the case where the support part 41 of the heat insulating part 14 is formed of a non-porous material such as SiO ₂ or Si ₃ N ₄ , the support part 41 occupying each pixel. The area ratio (opening ratio) of the temperature detector 13 occupying each pixel can be increased, and the volume of the temperature detector 13 can be increased. f Noise can be reduced, and as a result, the S / N ratio of the infrared sensor device can be improved.

  In addition, the infrared sensor IS can improve the heat insulation property and increase the sensitivity of each temperature detection unit 13 by setting the inside of a package (not shown) in a reduced pressure atmosphere.

(Embodiment 2)
The basic configuration of the infrared sensor device of the present embodiment is substantially the same as that of the first embodiment, and a thermopile infrared detector as shown in FIGS. 7A and 7B is used as the thermal infrared detector 1. Is different. Since other configurations are the same as those of the first embodiment, illustration and description thereof are omitted.

  The thermal infrared detecting element 1 in the present embodiment includes a base substrate 21 formed using a semiconductor substrate made of a silicon substrate, and a recess formed on one surface of the base substrate 21 (upper surface in FIG. 7A). A beam portion 24 spanned between two points on the peripheral portion of 21a, and an infrared absorption portion that is disposed apart from the one surface of the base substrate 21 in the thickness direction of the base substrate 21 and absorbs infrared rays and converts them into heat 25, the temperature sensing part 30 for detecting the temperature change of the infrared absorption part 25 on the one surface side of the base substrate 21, the intermediate part of the beam part 24 and the central part of the infrared absorption part 25 are mechanically and thermally connected. A coupling portion (joining column) 26 to be coupled is provided. FIG. 7A corresponds to the X-X ′ cross section of FIG.

  An insulating layer 22 is formed on one surface of the base substrate 21 described above, and the insulating layer 22 is a first insulating film 22 a made of a silicon oxide film formed on the one surface of the base substrate 21. And a second insulating film 22b made of a silicon oxide film stacked on the first insulating film 22a.

  In addition, the above-mentioned beam portion 24 includes a lower insulating film 24a formed integrally with the first insulating film 22a of the base substrate 21 and an upper portion formed integrally with the second insulating film 22b of the base substrate 21. It is comprised with the insulating film 24b. In short, the beam portion 24 is disposed inside the peripheral portion of the recess 21a in the base substrate 20 and is formed continuously and integrally with the peripheral portion of the recess 21a. Here, the beam portion 24 is formed in a meandering shape in a plane perpendicular to the thickness direction of the base substrate 21 (a bent shape in which a plurality of folds are bent in the plane), and both end portions are concave in the base substrate 21. It is connected with the peripheral part of the place 21a. Note that the second insulating film 22b and the upper insulating film 24b are not limited to the silicon oxide film, and may be formed of, for example, a silicon nitride film.

In the infrared absorbing portion 25, a first infrared absorbing layer 25 a and a second infrared absorbing layer 25 b each formed of an infrared absorbing material that absorbs infrared rays are stacked in the thickness direction of the base substrate 21. Here, the outer peripheral shape of the infrared absorbing portion 25 is formed in a rectangular shape, and the outer dimension is set larger than the rectangular inner peripheral shape of the recess 21 a on the one surface of the base substrate 21. As the infrared absorbing material of the infrared absorption layer 25a, 25b, but employs a SiON, not limited to SiON, for example, it may be _Si 3 _{N 4.}

  Further, as described above, the coupling portion 26 that couples the central portion of the infrared absorption portion 25 and the intermediate portion of the beam portion 24 is formed of a silicon oxide film, but is not limited to a silicon oxide film, and for example, silicon nitride You may comprise by a film | membrane.

  The temperature sensing unit 30 is an elongated thermopile in which a plurality of (here, two) thermocouples 31 made of pairs of semiconductor elements 31 a and 31 b of different conductivity types are connected in series and arranged along the beam portion 24. One cold junction part 30A is arranged in the peripheral part of the recess 21a in the base substrate 21 and two hot junction parts 30B are arranged in the middle part of the beam part 24. Here, each thermocouple 31 is formed by forming one of the paired semiconductor elements 31a and 31b with p-type polysilicon and the other with n-type polysilicon, and connecting one ends of the paired semiconductor elements 31a and 31b to each other. Are connected via a junction 31c made of a material having a higher thermal conductivity (for example, a metal material such as aluminum) than the material of each of the semiconductor elements 31a and 31b, and the pair of semiconductor elements 31a and 31b. Each one end part and the junction part 31c comprise the warm junction part 30B.

  In the temperature sensing unit 30, the other end of the semiconductor element 31b of one thermocouple 31 and the other end of the semiconductor element 31a of the other thermocouple 31 are connected via a joint 31d made of a metal material. The other end of the semiconductor element 31b of the one thermocouple 31, the other end of the semiconductor element 31a of the other thermocouple 31, and the junction 31d constitute a cold junction 30A. Here, the total length of each of the semiconductor elements 31 a and 31 b is set so that the cold junction portion 30 </ b> A is positioned in the peripheral portion of the recess 21 a in the base substrate 21. In the thermal infrared detecting element 1 of the present embodiment, since the semiconductor elements 31a and 31b are embedded in the beam portion 24 and the insulating layer 22, the first insulating film 22a and the lower insulating film are manufactured. After forming 24a, each of the semiconductor elements 31a and 31b is formed, and then the second insulating film 22b and the upper insulating film 24b are formed.

  By the way, in the thermal infrared detecting element 1 of the present embodiment, the cold junction portion 30A is arranged in the peripheral portion of the recess 21a in the base substrate 21 as described above, and the hot junction portion 30B is an intermediate portion of the beam portion 24. However, the warm contact portion 30B is positioned such that a part of the warm contact portion 30B is located farther from the one surface of the base substrate 21 in the thickness direction of the base substrate 21 than the cold contact portion 30A. It is in direct contact with the part 25. Specifically, in the thermal infrared detection element of the present embodiment, the cold junction 30A is embedded in the insulating layer 22, whereas the junction 31c in the hot junction 30B is formed in a U-shaped cross section. The leg pieces of the joint portion 31c are embedded in the thickness direction of the base substrate 21 so as to straddle the upper insulating film 24b, the coupling portion 26, and the first infrared absorption layer 25a, and the central piece is The base substrate 21 is embedded in the infrared absorbing portion 25 within a plane orthogonal to the thickness direction.

  In the thermal infrared detecting element 1 according to the present embodiment described above, a part of each of the hot contact portions 30B and 30B of the thermosensitive portion 30 made of a thermopile is formed in the base substrate 21 in the thickness direction of the base substrate 21 rather than the cold junction portion 30A. Since it is located away from the one surface of 21 and is in direct contact with the infrared absorbing portion 25, the heat of the infrared absorbing portion 25 is transferred to the hot junction portions 30B and 30B through the coupling portion 26. Thus, the temperature difference between the infrared absorbing part 25 and each of the hot contact parts 30B and 30B can be reduced, the sensitivity can be improved, and as a result, the S / N ratio of the infrared sensor device can be improved and the response speed can be improved. can do. Moreover, since a part of each warm junction part 30B, 30B is formed with the material whose heat conductivity is high compared with the material of each semiconductor element 31a, 31b, the infrared rays absorption part 25 and each warm junction part 30B, 30B. And the S / N ratio of the infrared sensor device can be improved.

1 is a block diagram of an infrared sensor device showing Embodiment 1. FIG. The thermal type infrared detecting element same as the above is shown, (a) is a schematic perspective view, (b) is an A-A 'schematic sectional view of (a). It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above. It is operation | movement explanatory drawing same as the above. The thermal infrared detection element in Embodiment 2 is shown, (a) is a schematic sectional drawing, (b) is a schematic sectional drawing different from (a). It is a schematic circuit diagram which shows a prior art example.

Explanation of symbols

IS infrared sensor 1 thermal infrared detection element 2 scanner 3 modulator 4 amplifier 5 signal separator 6 demodulator 7 analog low-pass filter 8 A / D converter 9 digital low-pass filter 10 multiplexer

Claims (2)

An infrared sensor that generates an output value of an analog amount corresponding to a temperature change due to infrared absorption, a modulator that modulates the output of the infrared sensor with a modulation signal having a frequency sufficiently higher than the frequency of the signal component, An amplifier for amplifying the output; a demodulator for extracting the output of the amplifier with a demodulated signal synchronized with the modulation signal; and a signal component of an infrared sensor provided at a subsequent stage of the demodulator with a cutoff frequency lower than the frequency of the demodulated signal An analog low-pass filter higher than the frequency range of the A / D converter, an A / D converter for analog-digital conversion of the output of the analog low-pass filter at a sufficiently high sampling frequency with respect to the frequency of the signal component of the infrared sensor, The cutoff frequency of the A / D converter is higher than the frequency range of the signal component of the infrared sensor. It and a digital low-pass filter is less than half of the ring frequency, infrared sensor is an array sensor having a plurality of thermal type infrared sensing device, a time in the modulator the output of each thermal type infrared sensing device A scanner for generating a scanning signal for sequential input; and a signal separator inserted between the amplifier and the demodulator for separating the output of the amplifier into an output corresponding to each thermal infrared detection element infrared sensor device characterized by comprising Te. 2. The infrared sensor device according to claim 1, wherein the thermal infrared detection element is a resistance bolometer type infrared detection element and synchronizes a scanning signal of the scanner and a modulation signal of the modulator .

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