JP3657885B2 - Infrared sensor device and driving method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an infrared sensor device and a driving method thereof, and more particularly to a signal readout circuit of a thermal infrared sensor and a driving method thereof. A low-noise, high-sensitivity, wide dynamic range thermal infrared sensor and a driving method thereof are provided.
[0002]
[Prior art]
Infrared imaging has the advantage of being able to capture images regardless of day and night, and has a higher permeability to smoke and fog than visible light. In addition, it can obtain temperature information on the subject. Wide application range as surveillance camera and fire detection camera.
[0003]
In recent years, the development of uncooled thermal infrared solid-state imaging devices that do not require a cooling mechanism for low-temperature operation, which is the biggest drawback of conventional quantum-type infrared solid-state imaging devices, has become active. . In a thermal infrared solid-state imaging device, an incident infrared ray having a wavelength of about 10 μm is converted into heat by an absorption structure, and the temperature change of the heat-sensitive part caused by the weak heat is converted into an electrical signal by some thermoelectric conversion means. The infrared image information is obtained by reading out the electrical signal.
[0004]
As a thermal infrared solid-state imaging device, a device in which a silicon pn junction that converts a temperature change into a voltage change by a constant forward current is formed in an SOI region has been reported (Tomohiro Ishikawa, et al., Proc. SPIE). Vol.3698, p.556, 1999).
[0005]
A silicon pn junction type element using an SOI substrate has a feature that it can be manufactured only by a silicon LSI manufacturing process, and is therefore an element excellent in mass productivity.
[0006]
Further, the silicon pn junction type element has a feature that the internal structure of the pixel can be simplified because the pn junction which is a thermoelectric conversion means has a pixel selection function utilizing the rectification characteristic of the pn junction. .
[0007]
By the way, although the temperature change of the pixel part in a thermal type infrared solid-state image sensor depends on the absorptivity of the infrared absorption layer and the optical system, it is generally 5 × 10 of the temperature change of the subject. ^-3 If the subject temperature changes by 1 [K], the pixel temperature changes by 5 [mK].
[0008]
When eight silicon pn junctions are connected in series to one pixel element, the thermoelectric conversion efficiency is about 10 [mV / K], so when the subject temperature changes by 1 [K], the pixel portion A signal voltage of 50 [μV] is generated.
[0009]
Actually, since it is often required to identify about 0.1 [K] as the temperature change of the subject, it is necessary to read a signal voltage of about 5 [μV] generated in that case.
[0010]
As described above, as a method for reading out a very weak signal voltage, a circuit configuration in which the generated signal voltage is current-amplified as a gate voltage of a MOS amplification transistor, and the amplified signal current is time-integrated with a storage capacitor is known. Yes.
[0011]
This circuit configuration is a circuit called a gate modulation integration circuit. This circuit configuration is arranged as a column amplifier circuit for each column of the matrix, and current amplification for one row is processed in parallel to limit the signal band. In addition, there is an effect that random noise can be reduced.
[0012]
The voltage gain G in the gate modulation integration circuit is determined by the mutual conductance of the amplification transistor: gm = δId / δVg, the integration time: ti, and the storage capacity: Ci, and is expressed by G = (ti × gm) / Ci.
When the integration time: ti and the storage capacity: Ci are given, the above gain is governed by the mutual conductance: gm of the amplification transistor, and gm when the n-type MOS transistor operates in the saturation region is expressed by the following equation (1). Is approximated by
gm = (W / L) · (εox / Tox) · μn · (Vgs−Vth) (1)
Where W: channel width, L: channel length, εox: gate oxide dielectric constant, Tox: gate oxide film thickness, μn: electron mobility, Vgs: gate-source voltage, Vth: transistor threshold voltage.
[0013]
As already described, since it is required to recognize about 0.1 [K] as the temperature difference of the subject, it is necessary to read out a signal of about 5 [μV] generated in the pixel portion at that time. However, this signal voltage level is a very low voltage as compared with a CMOS sensor which is a sensor for imaging general visible light. For example, Nakamura and Matsunaga, “High Sensitivity CMOS Image Sensor”, Journal of the Institute of Image Information and Television Engineers Vol. 54, no. 2, p. 216 and 2000, the noise voltage is about 0.4 [mV] = 400 [μV]. Compared with this, the noise level of the infrared sensor is as low as about 1/80 that of the CMOS sensor. The signal voltage to be handled is also a low voltage of about 1/80.
[0014]
Therefore, considering that the sensor output is processed by a circuit similar to a CMOS sensor that is a general image sensor, a column amplification circuit using a gate modulation integration circuit having a gain of about 80 times is required.
[0015]
[Problems to be solved by the invention]
By the way, in order to read out the temperature information of the thermoelectric conversion part as an electric signal, the thermal infrared sensor often has to pass a current through the thermoelectric conversion part. There is a so-called self-heating problem that Joule heat is generated in the thermoelectric converter due to the bias current or bias voltage for reading the temperature information, and the thermoelectric converter is heated by the Joule heat.
[0016]
For example, when a thermoelectric conversion pixel is incorporated in a semiconductor substrate, the thermal conductance with the semiconductor substrate is a typical value of 10 ^-7 [W / K] The effect of self-heating in the pn junction type thermoelectric converter is that the number of pn junctions is 8, the bias current is 200 [μA], and the pixel selection period for signal readout is 25 [μs]. When the frame rate is calculated as 60 [fps], the temperature rises by about 30 [K]. This temperature rise is very large when compared with the above-mentioned temperature rise of 5 [mK] due to the incidence of infrared rays, and it can be seen that the solution of this self-heating problem is very important.
[0017]
An example of pixel temperature change (voltage: Vsig conversion) due to self-heating is shown in FIG. As is apparent from the figure, the pixel temperature rapidly rises due to the pixel selection in the row selection period, and after the pixel selection pulse is turned off, it is gradually cooled by the thermal time constant of the thermoelectric conversion unit.
[0018]
According to the above calculation, the temperature change due to self-heating is 30 [K], and the temperature signal due to infrared incidence of only about 5 [mK] is at a level lower than the thickness of the curve in FIG. As a result, in a general column amplifier circuit connected to a signal line, a weak current flows at the initial stage of pixel selection, and the amount of signal current increases with time due to self-heating during pixel selection. In addition, most of the current component is a temperature information current caused by self-heating, that is, a noise current.
[0019]
An outline of the charges integrated and accumulated in the storage capacitor on the output side of the column amplifier circuit is schematically shown in FIG. 12 as a potential well diagram of the storage capacitor. As is apparent from the figure, most of the accumulated charge is charge Q due to self-heating. _SH The signal charge Qsig is slight.
[0020]
The figure also shows that as a result of the temperature change due to self-heating, the current in the second half of the pixel selection period is large, and as a result, information from the latter half of the pixel selection period is weighted. As a result, the effective sampling time is shortened, and the signal band is expanded, thereby causing an increase in random noise.
[0021]
X. Gu, et al. Have reported a method for avoiding the above-mentioned self-heating problem by constructing a bridge circuit when using a bolometer based on the temperature change of electrical resistance. X. Gu, et al., Sensors and Actuators A, Vol.69, p.92, 1998).
[0022]
They arrange reference insensitive pixels with the same heat capacity and low thermal resistance for each column, construct a bridge circuit, and perform differential amplification.
[0023]
This is a method utilizing the fact that the temperature rise due to self-heating in the pixel selection period, which is a very short time with respect to the thermal time constant, is mainly governed by the heat capacity.
[0024]
However, although this method has an effect of reducing the influence of self-heating, it is an approximate solution to the self-heating problem, and it cannot be said that the self-heating problem has been completely solved.
[0025]
In order to solve the strict self-heating problem, it is necessary to arrange the reference insensitive pixels one-to-one with respect to each sensitive pixel. Therefore, in an image sensor in which the pixels are laid out two-dimensionally. There is no real solution.
[0026]
This is because disposing the reference insensitive pixels constituting the bridge circuit in each pixel means that if the pixel size is the same, the demerit that the sensitivity is reduced to 1/2 or less occurs. Self-heating cancellation by a bridge circuit is not effective because of the advantages and disadvantages of the effects of solving the heating problem.
[0027]
In addition, this self-heating problem is not solved in a thermoelectric conversion pixel using a column amplifier circuit related to the technical field of the present invention, for example, a pn junction type infrared sensor. An object of the present invention is to solve such problems.
[0028]
[Means for Solving the Problems]
The first of the present invention is arranged in a matrix of a plurality of rows and columns, and a plurality of thermoelectric conversion pixels that take out heat generated by absorbing incident infrared light as thermoelectric conversion and change in resistance value;
A plurality of selection lines respectively connected to either one of each row or each column of the thermoelectric conversion pixels;
A plurality of signal lines respectively connected to the other of each row or each column of the thermoelectric conversion pixels;
Pixel selection means for generating a voltage output signal on the signal line by selectively applying a read voltage to the thermoelectric conversion pixel for each selection line connected to each of the selection lines;
An output signal amplifying means having a first input means and a second input means, wherein the first input means is connected to each signal line to amplify a voltage output signal from the thermoelectric conversion pixel;
A waveform connected to the second input means of the output signal amplifying means to cancel or reduce a voltage component included in the voltage signal due to a resistance change component accompanying self-heating generated by the read current in the thermoelectric conversion pixel. Compensation voltage applying means for applying a voltage in synchronization with the read voltage;
In an infrared sensor device comprising:
[0029]
The second of the present invention is a two-dimensional array on a semiconductor substrate, for absorbing incident infrared light and converting it into heat, and for converting a temperature change caused by heat generated in the absorption part into an electrical signal. A thermoelectric conversion pixel having thermoelectric conversion means;
A pixel selecting unit that is connected to the thermoelectric conversion pixel and selects the thermoelectric conversion pixel for reading a signal from the thermoelectric conversion pixel;
Pixel signal readout means for reading out signals from the thermoelectric conversion pixels selected by the pixel selection means;
Output means for outputting the signal read by the pixel signal reading means;
An infrared sensor device comprising:
The pixel readout means includes an amplifier circuit that amplifies a signal from the thermoelectric conversion pixel, the amplifier circuit has a MOS transistor, and at least the signal from the thermoelectric conversion pixel is applied to the gate of the MOS transistor as a voltage signal. Entered,
An infrared sensor device comprising: means for applying a ramp waveform voltage or a step waveform voltage synchronized with a pixel selection timing of the pixel selection means to a source of the MOS transistor so as to suppress an increase in the voltage signal It is in.
[0030]
According to the present invention, in the thermal infrared sensor, in order to solve the self-heating problem of the thermoelectric conversion unit due to Joule heat generated with pixel selection, the voltage signal from the thermoelectric conversion unit is input to the gate. A ramp waveform voltage or a step waveform voltage synchronized with the pixel selection pulse is applied to the source of the amplifying MOS transistor. As a result, the self-heating component voltage can be removed from the gate-source voltage Vgs of the amplification transistor, and an infrared sensor with high sensitivity, low noise, and wide dynamic range can be obtained.
[0031]
Furthermore, according to the present invention, a plurality of voltage generators are alternately operated every time one or more rows of pixels are selected, and a pulse waveform voltage having an appropriately long time constant is applied to the source of the MOS transistor. Thus, it is possible to remove the self-heating component voltage from the gate-source voltage: Vgs of the amplification transistor in the same manner as the ramp waveform voltage is applied, and an infrared sensor device with high sensitivity, low noise, and wide dynamic range can be obtained. it can.
[0032]
Further, according to the present invention, the insensitive pixel column having one or more thermally separated insensitive pixels arranged in each row is provided, and a voltage based on the output voltage from the insensitive pixel column is used as the amplification transistor. The self-heating component voltage can be removed from the gate-source voltage: Vgs of the amplification transistor in the same manner as the ramp waveform voltage is applied to the source of the high-sensitivity, low noise, wide dynamic range infrared sensor device Can be obtained.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is an overall configuration diagram of an infrared sensor device according to a first embodiment of the present invention, and shows a two-dimensional matrix configuration of m × n pixels of m rows and n columns (m and n are natural numbers of 2 or more).
[0034]
An infrared detection thermoelectric conversion pixel 1 that converts incident infrared light into an electrical signal is two-dimensionally arranged on a semiconductor substrate 2 to form an imaging region 3. Inside the imaging region 3, row selection lines 4 (4-1, 4-2...) And vertical column signal lines 5 (5-1, 5-2...) Are arranged. For pixel selection, a row selection circuit 40 and a column selection circuit 70 are arranged adjacent to each other in the row direction and the column direction of the imaging region 3, and are connected to the row selection line 4 and the column selection line 7, respectively.
[0035]
As the constant current source 80 for obtaining the pixel output voltage, load MOS transistors 8-1, 8-2... Are connected to the column signal line 5 of each column.
[0036]
In FIG. 1, the substrate voltage: Vs is applied to the source of the load MOS transistor. However, the source voltage can be adjusted as necessary, which is more preferable.
[0037]
In the row selected by the row selection circuit 40, the power supply voltage Vd is applied to the row selection line 4-4, for example, 4-1, and Vs is applied to the row selection line not selected by the row selection circuit 40. As a result, the pn junction region 115 inside the thermoelectric conversion pixel 1 in the selected row 4-1 becomes a forward bias and a bias current flows, and the operating point is determined by the temperature of the pn junction inside the pixel and the forward bias current, A pixel signal output voltage is generated on the column signal lines 5-1 and 5-2 of each column. At this time, the pn junction regions 115a of the pixels not selected by the selection circuit 40 are reverse-biased. That is, the pn junction inside the pixel has a pixel selection function.
[0038]
The voltage generated in the column signal line 5 is extremely low, and the ratio of the subject temperature change: dTs to the pixel temperature change: dTd is 5 × 10. ^-3 Assuming that this value and the pn junction of the pixel are 8 pn junctions connected in series, the thermoelectric conversion sensitivity: dV / dTd = 10 [mV / K], and when dTs = 0.1 [K] It can be seen that it is only 5 [μV].
[0039]
Therefore, in order to recognize this subject temperature difference, it is necessary to reduce the noise generated in the column signal line to 5 [μV] or less. The value of this noise is as low as about 1/80 of the noise of a CMOS sensor which is a MOS type visible light image sensor.
A column amplifier circuit 9 is connected between the signal lines 5-1 and 5-2 and the column selection transistor group 60, and each signal line is connected to the gate 10 g of the amplification MOS transistor 10 of the amplifier circuit. A storage capacitor 12 for integrating and storing the signal current amplified is connected to the drain 10d side of the MOS transistor 10. The accumulation time for integrating the signal current is determined by the row selection pulse applied to the row selection line 4 by the row selection circuit 40.
[0040]
The storage capacitor 12 is connected to a reset transistor 14 for resetting the voltage of the storage capacitor, and the reset operation is performed after the signal voltage is read by the column selection transistor 6. Terminal 24 is an output terminal.
[0041]
2A and 2B illustrate the structure of the infrared detection thermoelectric conversion pixel 1 according to the present embodiment. FIG. 2A is a plan view and FIG. 2B is a cross-sectional view. The thermoelectric conversion pixel 1 including the pn junction region 115 for thermoelectric conversion is formed on the hollow structure 107 formed inside the single crystal silicon semiconductor substrate 106 and the infrared absorption portions 118 and 120 and for thermoelectric conversion. It comprises a pn junction region 115 inside the SOI layer 108, a wiring 117 connecting them, and a thermoelectric conversion part 110 of a buried silicon oxide film layer 114 that supports the SOI layer 108. In the figure, a diode structure in which two pn junction regions are arranged is shown for explanation. Further, the support unit 111 for supporting the pixel 1 via the hollow bottom portion 107 and the hollow side portion 119 having a hollow structure and outputting an electric signal from the pixel 1, the pixel 1, the column signal line 5, and the row selection line. 4 comprises a connecting portion (not shown) for connecting to 4. By providing the pixel 1 and the support portion 111 on the hollow structure 107, the heat dissipation of the pixel is slow, and the temperature of the element 1 is efficiently modulated by incident infrared rays.
[0042]
A manufacturing method for realizing such a structure is described in detail in prior patent applications relating to the inventors' invention, such as Japanese Patent Application No. 2000-298277 and Japanese Patent Application No. 2000-095678.
[0043]
In the first embodiment of the present invention, as shown in FIG. 1, a voltage generator 300 is mounted on a semiconductor substrate. The voltage generator 300 is connected to a row selection circuit 40 at a terminal 21 and a row selection pulse is received. When input, a ramp waveform voltage as shown in FIG. 3 synchronized with the row selection pulse is generated in the row selection period, and the source voltage of the source 10s of the amplification transistor 10 in the column amplifier circuit 9 is supplied as an input. It is.
The temperature increase due to the self-heating of the pixel already described is shown in FIG. 11, and the thermal time constant of this temperature increase is determined by the thermal separation of the thermoelectric conversion pixel 1 and is generally on the order of [ms].
[0044]
On the other hand, as shown in FIG. 11, since the row selection period is on the order of [μs], it is very short compared to the thermal time constant, and in fact, linear approximation is sufficiently possible in this row selection period. Therefore, the voltage of the self-heating component generated in the column signal line 5 applied to the gate 10g of the amplification transistor 10 is canceled and canceled by applying the above ramp waveform voltage to the source 10s of the amplification transistor 10, so that Only the signal of the temperature change component due to the incident can be amplified.
[0045]
As a result, the operating point of the amplifying transistor 10 is optimized, current amplification of only the signal component having no self-heating component is possible, gain can be improved, and random noise due to band expansion increases. There is no end to it. Therefore, an infrared sensor having high sensitivity, low noise, and a wide dynamic range can be obtained.
[0046]
In the second embodiment of the present invention, a voltage generator 300 for generating a step waveform voltage in FIG. 1 is mounted on a semiconductor substrate. The voltage generator 300 receives a row selection pulse from the row selection circuit 40. By inputting, a step waveform voltage synchronized with the row selection pulse is generated as shown in FIG. 4 and supplied as the source voltage of the amplification transistor 10 in the column amplifier circuit 9 as the second input.
[0047]
In order to generate the step waveform voltage, for example, a D / A conversion circuit can be used. By setting the number of bits appropriately, an effect substantially equivalent to the case where the ramp waveform voltage is applied is obtained. be able to. In addition, there is an advantage that the waveform line can be finely adjusted.
[0048]
Therefore, as in the first embodiment, the voltage of the self-heating component applied to the gate of the amplification transistor 10 as the first input and generated in the column signal line 5 is differentially described in a direction to suppress the increase. Is applied to the source of the amplifying transistor 10, and only the signal of the temperature change component due to the incidence of infrared light can be amplified.
[0049]
As a result, the operating point of the amplifying transistor 10 is optimized, current amplification of only the signal component without the self-heating component is possible, gain can be improved, and random noise due to the aforementioned band expansion increases. There is no end to it. Therefore, an infrared sensor having high sensitivity, low noise, and a wide dynamic range can be obtained.
[0050]
Furthermore, as a modification of the first and second embodiments, the voltage generator 300 can be mounted outside the semiconductor substrate. The voltage generator 300 generates a ramp waveform or a step waveform voltage synchronized with the row selection pulse as shown in FIGS. 3 and 4 by inputting the row selection pulse from the row selection circuit 40 from the row selection pulse output unit 21. Then, the source voltage of the amplification transistor 10 in the column amplifier circuit 9 is supplied to the amplification transistor source voltage input unit 22 on the semiconductor substrate via the wiring 23.
[0051]
Therefore, as in the first and second embodiments, the voltage of the self-heating component generated in the column signal line 5 applied to the gate of the amplification transistor 10 applies the above step waveform voltage to the source 10 s of the amplification transistor 10. By doing so, it becomes possible to amplify only the signal of the temperature change component due to the incidence of infrared rays.
[0052]
As a result, the operating point of the amplifying transistor 10 is optimized, current amplification of only the signal component without the self-heating component is possible, gain can be improved, and random noise due to the aforementioned band expansion increases. There is no end to it.
[0053]
Next, a third embodiment of the present invention is shown in FIGS. 1 denote the same parts. This embodiment is the same as the configuration shown in FIG. 1 except that the voltage generator 301 generates a rectangular wave voltage and an integration circuit 302 is disposed between the source voltage input terminals 22 of the amplification transistors. This voltage generator 301 is mounted inside the semiconductor substrate, and the rectangular wave voltage V1 synchronized with the row selection pulse by inputting the row selection pulse from the row selection circuit 40 from the row selection pulse output unit 21 (FIG. 6A). Is generated.
[0054]
In the present embodiment, an integration circuit 302 including an electric capacitance 303 is provided on the wiring 23 between the voltage generator 301 and the amplification transistor source voltage input unit 22 on the semiconductor substrate. As shown in FIG. 6A, when a rectangular wave voltage pulse V1 synchronized with the row selection pulse is input to the integrating circuit 302, the integrating circuit 302 becomes the integrated waveform voltage V2 shown in FIG. The source voltage of the amplification transistor 10 in the column amplifier circuit 9 is supplied to the upper amplification transistor source voltage input unit 22. This integral ramp waveform can be approximated to the voltage of the self-heating component included in the input signal of the amplification transistor, and therefore is applied to the gate 10g of the amplification transistor 10 as in the first and second embodiments. The voltage of the self-heating component generated in the column signal line 5 is canceled by applying the above integrated waveform voltage to the source of the amplification transistor 10, and only the signal of the temperature change component due to the incidence of infrared light can be amplified. .
[0055]
As a result, the operating point of the amplifying transistor 10 is optimized, current amplification of only the signal component without the self-heating component is possible, gain can be improved, and random noise due to the aforementioned band expansion increases. There is no end to it.
[0056]
As a modification of the third embodiment, the voltage generator 301 and the integration circuit 302 can be mounted outside the sensor chip.
[0057]
7 and 8 show a fourth embodiment. 1 denote the same parts. In this embodiment, the pixels are grouped every other row into two groups, for example, divided into two groups of odd rows and even rows, and the first group of voltage generators 304 and the second group of voltage generators 305 are operated alternately. It is something to be made. In this embodiment, a sampling hold (S / H) circuit for 1H period is added for the purpose of reducing random noise, and most of the 1H period is driven as a row selection period, that is, a pixel selection period as shown in FIG.
[0058]
Alternatively, a circuit configuration in which the signal charge accumulated by the column amplification operation is moved to the added sample and hold circuit and output at a timing delayed by one row is also possible. In this case, all rows are the same. Processing by the circuit is more preferable because generation of fixed pattern noise such as so-called horizontal stripes every other line can be suppressed.
[0059]
In the case of such driving, depending on the time constant set by the additional capacitance, the non-selection period t1 of the pixel selection pulses in two consecutive rows is short, so that amplification on the semiconductor substrate is performed as shown in FIG. The voltage Vs ′ at the transistor source voltage input section is not sufficiently lowered as Vs ″, and the transistor does not operate normally.
[0060]
Therefore, in that case, a plurality of voltage generators 304 and 305 corresponding to the two groups are provided, and a plurality of amplification transistor source voltage input units 22 are provided to perform switching every other row. As a result, when two voltage generators 304 and 305 are provided, the voltage Vs having the waveform shown in FIGS. 8B and 8C is alternately output every other row, and also inside the sensor chip. The voltages Vs and Vs shown in FIGS. 8B and 8C are supplied as the source voltage of the amplification transistor in the column amplifier circuit 90 every other row.
[0061]
Therefore, as in the first to third embodiments, the voltage of the self-heating component generated in the column signal line 5 applied to the gate 10g of the amplification transistor 10 is the above step waveform voltage applied to the source 10s of the amplification transistor 10. It is canceled out by the application, and it becomes possible to amplify only the signal of the temperature change component due to the incident infrared rays.
[0062]
As a result, the operating point of the amplifying transistor 10 is optimized, current amplification of only the signal component without the self-heating component is possible, gain can be improved, and random noise due to the aforementioned band expansion increases. There is no end to it. Therefore, an infrared sensor having high sensitivity, low noise, and a wide dynamic range can be obtained.
[0063]
A fifth embodiment of the present invention will be described with reference to FIGS. 9 and 10. The thermoelectric conversion pixel 1 is the same as the hollow support structure of the pn junction region described in FIG. 2, and also includes a constant current source 80 using a load transistor, a row selection circuit 40, a row selection line 4, a column selection circuit 70, Since the column signal line 5, the column selection transistor group 60, the column amplifier circuit group 90, and the like are the same as those in FIG. 1, the description thereof is omitted.
[0064]
In the present embodiment, as shown in FIG. 9, the last column of the pixel matrix is provided as a thermal separation insensitive pixel column 500, and the thermal separation insensitive pixels 501 are distributed and provided in each row. The structure of the thermal separation insensitive pixel 501 is almost the same as the pixel structure of FIG. 2 as shown in FIG. 10, but the infrared reflection layer 130 of a metal film such as aluminum is provided on the infrared absorption layer 118 only. Is different.
[0065]
In this heat-separated insensitive pixel 501, the incident infrared light is reflected by the infrared reflection layer 130, and a temperature change due to the incidence of infrared light does not occur, and only a self-heating signal based on pixel selection is output to the column signal line 502.
[0066]
The column signal line output from the thermal separation insensitive pixel column 500 is converted into the source voltage of the amplification transistor 10 (see FIG. 1) in the column amplification circuit 90 via the source follower circuit 400 as shown in FIG. It becomes possible to supply as.
[0067]
Needless to say, the operating point can be optimized by appropriately adjusting the voltages at the terminals 401 and 402 of the source follower circuit. Therefore, as in the first to fourth embodiments, the voltage of the self-heating component generated in the column signal line 5 in the output signal applied to the gate of the amplification transistor 10 is the waveform voltage of the column signal line. Application to the source input section 22 of the amplifying transistor 10 cancels out with high accuracy, and it becomes possible to amplify only a signal of a temperature change component due to infrared incidence. By mounting insensitive pixels on the same semiconductor substrate, the self-heating component is output as a voltage having almost the same tendency, so that the obtained waveform can be applied as it is.
[0068]
As a result, the operating point of the amplifying transistor 10 is optimized, current amplification of only the signal component without the self-heating component is possible, gain can be improved, and random noise due to the aforementioned band expansion increases. There is no end to it. Therefore, an infrared sensor having high sensitivity, low noise, and a wide dynamic range can be obtained.
[0069]
Note that although FIG. 9 illustrates the case where the one-stage source follower circuit 400 is provided, it can be changed to a plurality of stages of source follower circuits as necessary.
[0070]
Further, the circuit 400 is not limited to the source follower circuit, and can be appropriately changed as long as it does not affect the thermal separation insensitive pixel column signal line output voltage.
[0071]
As described above, the present invention has been described by using the column amplifier circuit configured as a single amplifier MOS transistor having the first input as the gate and the second input as the source as the output signal amplifier according to the embodiment. Since this amplifier circuit has a simple configuration, it is preferable for manufacturing. However, other amplifier circuits such as a differential amplifier can be used as long as they have two inputs.
[0072]
Further, the thermoelectric conversion pixel has been described using a pn junction in the present embodiment, but the present invention is not limited thereto, and an infrared sensor device including a thermoelectric conversion pixel using a bolometer such as vanadium oxide, for example. It is also applicable to.
[0073]
In that case, it goes without saying that a selection transistor for pixel selection is required in each pixel.
[0074]
In addition, various modifications can be made without departing from the scope of the present invention.
[0075]
【The invention's effect】
According to the present invention, a thermal infrared sensor having high sensitivity, low noise, and a wide dynamic range can be obtained.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram of first and second embodiments of the present invention.
FIGS. 2A and 2B illustrate a thermoelectric conversion pixel according to first and second embodiments, in which FIG. 2A is a plan view, and FIG. 2B is a cross-sectional view taken along line AA in FIG.
FIGS. 3A and 3B are waveform diagrams illustrating the first embodiment. FIG.
FIGS. 4A and 4B are waveform diagrams illustrating a second embodiment.
FIG. 5 is a configuration diagram of a third embodiment of the present invention.
FIGS. 6A and 6B are waveform diagrams illustrating a third embodiment of the present invention.
FIG. 7 is a configuration diagram of a fourth embodiment of the present invention.
FIGS. 8A, 8B, and 8C are waveform diagrams illustrating a fourth embodiment of the present invention.
FIG. 9 is a schematic configuration diagram of a fifth embodiment of the present invention.
FIGS. 10A and 10B illustrate a thermoelectric conversion pixel according to a fifth embodiment, in which FIG. 10A is a plan view and FIG. 10B is a cross-sectional view taken along line AA in FIG.
FIG. 11 is a diagram for explaining how the pixel temperature Td and the output signal voltage Vsig change suddenly due to self-heating in the row selection period, and the pixel temperature returns to the original state over one frame period.
FIG. 12 shows a signal charge Qsig and noise charge Q caused by self-heating in the storage capacitor in the column amplifier circuit. _SH Is a potential well diagram schematically showing a state of being accumulated during the pixel selection period.
[Explanation of symbols]
1 ... Thermoelectric conversion pixel
2 ... Semiconductor substrate
3 ... Imaging area
4 ... Row selection line
5 ... Column signal line
6 ... Column selection transistor
7 ... Column selection line
8 ... Load transistor
9 ... Column amplification circuit
10 ... MOS amplification transistor
12 ... Storage capacity
14 ... Reset transistor
21 ... Pixel selection pulse output section
22 ... Source voltage input section of amplification transistor
23 ... Wiring
24 ... Signal output section
40. Row selection circuit
60: Column selection transistor group
70 ... Column selection circuit
80 ... Constant current circuit
90 ... column transistor group
106: Semiconductor substrate
107: hollow bottom
108 ... SOI layer
110 ... thermoelectric conversion part
111 ... Support legs
114 ... buried oxide film
115 ... pn junction region
117 ... Wiring
118 ... Infrared absorbing part
119: Hollow side part
120: Infrared absorber
130: Infrared reflective layer
300 ... Voltage generator
400: Source follower circuit
401: Source follower circuit terminal
402: Source follower circuit terminal
500 ... Thermal separation insensitive pixel array
501 ... Thermal separation insensitive pixel

Claims (9)

A thermoelectric device that is two-dimensionally arranged on a semiconductor substrate and has an infrared absorber for absorbing incident infrared light and converting it into heat, and thermoelectric conversion means for converting a temperature change caused by the heat generated in the absorber into an electrical signal. A conversion pixel, connected to the thermoelectric conversion pixel, for reading a signal from the thermoelectric conversion pixel, Pixel selection means for selecting the thermoelectric conversion pixel, pixel signal reading means for reading a signal from the thermoelectric conversion pixel selected by the pixel selection means, and outputting the signal read by the pixel signal reading means Output means, wherein the pixel signal readout means includes an amplifier circuit for amplifying a signal from the thermoelectric conversion pixel, the amplifier circuit having a MOS transistor, and at least the thermoelectric conversion An output signal from the pixel is input as a voltage signal to the gate of the MOS transistor, and a ramp waveform voltage or a step waveform voltage synchronized with the pixel selection timing of the pixel selection means is added to the source of the MOS transistor. And an infrared sensor device characterized by comprising: . As a means for applying the ramp waveform voltage or the step waveform voltage, a voltage generator for generating a ramp waveform voltage or a step waveform voltage in synchronization with a pixel selection pulse from the pixel selection means is formed on the semiconductor substrate. The infrared sensor device according to claim 1, wherein As means for applying the ramp voltage or step waveform voltage, a voltage generator for generating a ramp waveform voltage or step waveform voltage synchronized with a pixel selection pulse from the pixel selection means is provided outside the semiconductor substrate. The infrared sensor device according to claim 1. The pixel selection means includes a pixel selection pulse output terminal, and a voltage generator that generates a rectangular wave voltage in synchronization with the pulse output is provided outside the semiconductor substrate. A rectangular wave voltage output from the voltage generator is provided. 2. The infrared sensor according to claim 1, wherein an integrating circuit including at least one electric capacitance is added to a current path between the output terminal of the voltage generator and the source. apparatus. The infrared sensor device according to claim 4, comprising a plurality of the voltage generators. Two-dimensionally arranged in multiple rows and columns on a semiconductor substrate to absorb incident infrared light and convert it into heat, and to convert temperature changes due to heat generated in this absorption portion into electrical signals A thermoelectric conversion pixel, and a thermoelectric conversion pixel having a support structure for supporting the infrared absorption part and the thermoelectric conversion part on a hollow structure formed inside the semiconductor substrate. Includes at least a wiring for reading a signal from the thermoelectric conversion unit, and the wiring is connected to a row selection line and a column signal line, and a pixel selection pulse for reading a signal from the thermoelectric conversion pixel is received. Pixel selection means for selecting the thermoelectric conversion pixels by applying to each row selection line, and pixels for reading signals from the thermoelectric conversion pixels selected by the pixel selection means from the column signal lines An infrared sensor device comprising: a signal reading means; and an output means for outputting a signal from the thermoelectric conversion pixel read by the reading means, wherein the pixel reading means is a signal from the thermoelectric conversion pixel. A circuit for performing current modulation by applying at least a signal from the thermoelectric conversion pixel as a voltage signal to the gate of the MOS transistor, and optically infrared-sensitive. In addition, at least one thermal separation insensitive pixel supported by the support leg on the hollow structure is provided in each row on the semiconductor substrate, and the thermal separation insensitive pixel is arranged as an insensitive pixel column. A voltage based on the insensitive column signal line voltage generated in the column signal line of the insensitive pixel column Infrared sensor device characterized by comprising comprises a means for inputting the source of register. 2. A source follower circuit having at least one stage of a reference voltage generated from the thermal separation insensitive pixel as an input, and an output of the source follower circuit being input to a source of the MOS transistor. 6. The infrared sensor device according to 6. The thermal separation insensitive pixel is red on the surface of the infrared absorption part inside the thermoelectric conversion pixel. The infrared sensor device according to claim 6, further comprising an external reflection layer. An infrared absorption part arranged two-dimensionally on a semiconductor substrate for absorbing incident infrared light and converting it into heat, and a thermoelectric conversion part for converting a temperature change caused by heat generated in the absorption part into an electrical signal A thermoelectric conversion pixel having a support structure for supporting the thermoelectric conversion unit on a hollow structure formed inside the semiconductor substrate, and reading at least signals from the thermoelectric conversion unit to the support structure Wiring for including a pixel selection means for selecting the thermoelectric conversion pixel for reading a signal from the thermoelectric conversion pixel, and reading a signal from the thermoelectric conversion pixel selected by the pixel selection means A pixel signal reading means for outputting the pixel signal, and an output means for outputting a signal from the thermoelectric conversion pixel read by the reading means. The means includes a MOS transistor amplifying circuit for amplifying a signal from the thermoelectric conversion pixel, and the amplifying circuit performs current modulation by applying at least a signal from the thermoelectric conversion pixel as a voltage signal to the gate of the MOS transistor. A method of driving an infrared sensor which is a circuit including a circuit for performing an infrared sensor, wherein a ramp waveform voltage or a step waveform voltage synchronized with a selection pulse of the thermoelectric conversion pixel is applied to a source of the MOS transistor. Driving method.

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