Imaging device

Abstract

A plurality of pixels (2) are formed in a matrix on a semiconductor chip (1). Each pixel (2) has an adjacent hollow pixel (3) and a non-hollow reference pixel (4). A differential amplifier (6) amplifies the difference in output voltage between the adjacent hollow pixel (3) and non-hollow reference pixel (4).

Description

[Technical Field]

[0001] The present disclosure relates to an imaging device. [Background technology]

[0002] The pixel array of the image pickup device has identical pixels arranged in a matrix. An image pickup device has been proposed that includes an environmental temperature detection unit that senses changes in chip temperature, so that the output voltage is set to a value that corresponds to the environmental conditions (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2006-314025 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventionally, the ambient temperature sensor was located at the edge of the chip, away from the pixel array, resulting in a temperature difference between the ambient temperature sensor and the pixel array, reducing measurement accuracy. Consequently, it was not possible to cancel out the temperature distribution and process variations within the chip surface. This resulted in increased fixed pattern noise (FPN) and increased the ENOB required by the AD converter connected downstream. Furthermore, calibration was required to adjust the voltage output by each pixel to be consistent across the surface with the shutter closed. While pixel output voltage needs to be stable during calibration, changes in chip temperature typically result in changes in output voltage. For this reason, even when performing calibration using the shutter during transitional chip temperatures, such as when the device is turned on or exposed to sunlight, the subject temperature could not be correctly output.

[0005] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to obtain an imaging device that can mitigate the effects of chip-surface variations and chip temperature transitions. [Means for solving the problem]

[0006] The imaging device according to the present disclosure includes a semiconductor chip, a plurality of pixels formed in a matrix on the semiconductor chip, a differential amplifier, and , current source and Each pixel has a hollow pixel and a non-hollow reference pixel adjacent to each other, and the differential amplifier amplifies an output voltage difference between the adjacent hollow pixel and the non-hollow reference pixel. The current source supplies bias current to the hollow pixel and the non-hollow reference pixel, and the current source makes the bias current of the non-hollow reference pixel lower than the bias current of the hollow pixel so that a difference in output voltage between the hollow pixel and the non-hollow reference pixel becomes small when infrared light is not incident. It is characterized by: Another imaging device according to the present disclosure includes a semiconductor chip, a plurality of pixels formed in a matrix on the semiconductor chip, a differential amplifier, and an inverting averaging circuit connected downstream of the differential amplifier, wherein each pixel has a hollow pixel and a non-hollow reference pixel adjacent to each other, the differential amplifier amplifies an output voltage difference between the adjacent hollow pixel and the non-hollow reference pixel, the hollow pixels include a first hollow pixel and a second hollow pixel, the non-hollow reference pixels include a first non-hollow reference pixel adjacent to the first hollow pixel and a second non-hollow reference pixel adjacent to the second hollow pixel, and the The differential amplifier has a first input terminal and a second input terminal, the differential amplifier inputs the output voltage of the first hollow pixel from the first input terminal and the output voltage of the first non-hollow reference pixel from the second input terminal, and outputs a first output signal, the differential amplifier inputs the output voltage of the second hollow pixel from the second input terminal and the output voltage of the second non-hollow reference pixel from the first input terminal, and outputs a second output signal, and the inverting and averaging circuit calculates the average of an inverted version of the first output signal and the second output signal. [Effects of the Invention]

[0007] In the present disclosure, a non-hollow reference pixel is arranged adjacent to a hollow pixel in each pixel, and the output voltage difference between them is calculated, thereby mitigating the effects of chip-wide variations such as process variations or temperature variations and chip temperature transitions. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a plan view showing an imaging device according to a first embodiment. [Figure 2] 1 is a circuit diagram illustrating an imaging device according to a first embodiment. [Figure 3] FIG. 1 is a cross-sectional view showing a hollow pixel. [Figure 4] FIG. 10 is a cross-sectional view showing a non-hollow reference pixel. [Figure 5] FIG. 10 is a diagram showing the output voltage of a hollow pixel. [Figure 6] FIG. 10 is a diagram showing the output voltages of a hollow pixel and a non-hollow reference pixel when the same bias current is applied. [Figure 7] 5 is a diagram showing output voltages of hollow pixels and non-hollow reference pixels according to the first embodiment. FIG. [Figure 8] FIG. 10 is a plan view showing an imaging device according to a second embodiment. [Figure 9] FIG. 10 is a diagram illustrating a subsequent stage of a differential amplifier in an imaging device according to a second embodiment. [Figure 10]FIG. 10 is a diagram illustrating functions of an imaging device according to a second embodiment. [Figure 11] FIG. 11 is a plan view showing an imaging device according to a third embodiment. [Figure 12] FIG. 10 is a circuit diagram illustrating an imaging device according to a fourth embodiment. [Figure 13] FIG. 11 is a plan view showing an imaging device according to a fifth embodiment. [Figure 14] FIG. 13 is a plan view showing a modified example of the imaging device according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] An imaging device according to an embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.

[0010] Embodiment 1 Fig. 1 is a plan view showing an imaging device according to embodiment 1. Fig. 2 is a circuit diagram showing the imaging device according to embodiment 1. This imaging device is an infrared sensor that detects infrared rays. A plurality of pixels 2 are formed in a matrix on a semiconductor chip 1. Each pixel 2 has a hollow pixel 3 and a non-hollow reference pixel 4 adjacent to each other.

[0011] A current source 5 supplies bias currents individually to the hollow pixels 3 arranged in a row and the non-hollow reference pixels 4 arranged in a row. A first input terminal IN1 of a differential amplifier 6 is connected to the output of the hollow pixels 3 arranged in a row. A second input terminal IN2 of the differential amplifier 6 is connected to the output of the non-hollow reference pixels 4 arranged in a row. When switch Row1 is turned on, the hollow pixels 3 and non-hollow reference pixels 4 in the corresponding row become active and output an output voltage. Similarly, when switch Row2 is turned on, the hollow pixels 3 and non-hollow reference pixels 4 in the corresponding row become active and output an output voltage. The differential amplifier 6 amplifies the difference in output voltage between adjacent hollow pixels 3 and non-hollow reference pixels 4.

[0012] 3 is a cross-sectional view showing a hollow pixel. The semiconductor chip 1 is, for example, a silicon substrate. An oxide film 7 is formed on the surface of the semiconductor chip 1. A recess 8 is formed in part of the surface of the semiconductor chip 1. A hollow pixel 3 is disposed above the recess 8 in a hollow state. The hollow pixel 3 is a diode that is vacuum-insulated from the semiconductor chip 1.

[0013] 4 is a cross-sectional view showing a non-hollow reference pixel. The non-hollow reference pixel 4 is in contact with the semiconductor chip 1 via an oxide film 7 and is thermally connected to the semiconductor chip 1. This allows the non-hollow reference pixel 4 to easily dissipate heat. As a result, the non-hollow reference pixel 4 does not experience temperature increases due to self-heating or infrared radiation, and the diode of the non-hollow reference pixel 4 generates a potential difference corresponding to the temperature of the semiconductor chip 1. Therefore, the non-hollow reference pixel 4 functions as a reference voltage generation circuit that outputs a voltage corresponding to the chip temperature.

[0014] Figure 5 shows the output voltage of a hollow pixel. Because the area around the hollow pixel 3 is in a vacuum state, heat dissipation from the hollow pixel 3 to the semiconductor chip 1 is suppressed. Therefore, when a bias current Ibias1 is passed through the hollow pixel 3 and infrared light is irradiated from an object, the temperature of the hollow pixel 3 rises due to self-heating and infrared radiation, and the potential difference across the diode of the hollow pixel 3 changes from Vref1 to V1. This makes it possible to measure the temperature of the object.

[0015] Figure 6 shows the output voltages of a hollow pixel and a non-hollow reference pixel when the same bias current is applied. By calculating the output voltage difference between the adjacent hollow pixel 3 and non-hollow reference pixel 4, the effects of the temperature of the semiconductor chip 1 can be eliminated and a potential difference corresponding to the temperature of the subject can be output. However, if the same bias current Ibias1 is applied to the hollow pixel 3 and the non-hollow reference pixel 4, the temperature rise of the diode in the insulated hollow pixel 3 due to self-heating will be greater than the temperature rise of the diode in the non-hollow reference pixel 4. As a result, the potential difference input to the downstream differential amplifier 6 will be too large, which can cause the output of the differential amplifier 6 to saturate.

[0016] 7 is a diagram showing the output voltages of hollow pixels and non-hollow reference pixels according to embodiment 1. The current source 5 sets the bias current Ibias2 of the non-hollow reference pixels 4 lower than the bias current Ibias1 of the hollow pixels 3 so that the difference between the output voltages of the hollow pixels 3 and the non-hollow reference pixels 4 when no infrared light is incident is small. This reduces the potential difference input to the differential amplifier 6, thereby preventing saturation of the differential amplifier 6. It is preferable that the current source 5 adjusts the bias currents Ibias1 and Ibias2 so that the output voltages of the hollow pixels 3 and the non-hollow reference pixels 4 are the same when no infrared light is incident.

[0017] As described above, in this embodiment, the non-hollow reference pixel 4 is arranged adjacent to the hollow pixel 3 in each pixel 2, and the output voltage difference between them is calculated. This makes it possible to mitigate the effects of chip-surface variations such as process variations and temperature variations, and chip temperature transitions.

[0018] Furthermore, the non-hollow reference pixel 4 has the same diode structure as the hollow pixel 3, with the diode of the hollow pixel 3 changed to a non-hollow type. This causes the hollow pixel 3 and the non-hollow reference pixel 4 to change in the same way in response to process fluctuations, making them less susceptible to the effects of process variations within the chip surface. Furthermore, the elimination of variations within the chip surface makes calibration using a shutter unnecessary.

[0019] Embodiment 2 8 is a plan view showing an imaging device according to embodiment 2. Each pixel 2 is divided into a first region 2a and a second region 2b. When the size of each pixel is 50 x 50 μm, the size of the first region 2a and the second region 2b are each 50 x 25 μm.

[0020] The hollow pixel 3 includes a first hollow pixel 3a and a second hollow pixel 3b. The non-hollow reference pixel 4 includes a first non-hollow reference pixel 4a adjacent to the first hollow pixel 3a and a second non-hollow reference pixel 4b adjacent to the second hollow pixel 3b.

[0021] The first hollow pixel 3a and the first non-hollow reference pixel 4a are formed in the first region 2a. The second hollow pixel 3b and the second non-hollow reference pixel 4b are formed in the second region 2b in the reverse order to the first hollow pixel 3a and the first non-hollow reference pixel 4a. The first hollow pixel 3a and the second non-hollow reference pixel 4b are connected to a first input terminal IN1. The second hollow pixel 3b and the first non-hollow reference pixel 4a are connected to a second input terminal IN2.

[0022] Hollow pixels 3 and non-hollow reference pixels 4 are mixed in the same column. Therefore, the current source 5 switches the bias current Ibias1 and bias current Ibias2 using a cross switch, thereby making the bias current of the non-hollow reference pixels 4 lower than the bias current of the hollow pixels 3, as in the first embodiment.

[0023] When switch Row1 is turned on, the differential amplifier 6 receives the output voltage of the first hollow pixel 3a through the first input terminal IN1 and the output voltage of the first non-hollow reference pixel 4a through the second input terminal IN2, and outputs a first output signal. When switch Row2 is turned on, the differential amplifier 6 receives the output voltage of the second hollow pixel 3b through the second input terminal IN2 and the output voltage of the second non-hollow reference pixel 4b through the first input terminal IN1, and outputs a second output signal.

[0024] FIG. 9 is a diagram showing the rear stage of the differential amplifier of the imaging device according to the second embodiment. An AD converter 9 and an inverting averaging circuit 10 are connected to the rear stage of the differential amplifier 6. The AD converter 9 and the inverting averaging circuit 10 can be configured as an ASIC or can be built into the sensor IC. The AD converter 9 converts the magnitude of the output voltage of the differential amplifier 6 into a digital signal. The digitized first output signal is input to terminal A of the inverting averaging circuit 10, and the second output signal is input to terminal B of the inverting averaging circuit 10. The inverting averaging circuit 10 calculates the average of the inverted first output signal of the differential amplifier 6 and the second output signal.

[0025] FIG. 10 is a diagram illustrating the functions of an imaging device according to the second embodiment. Due to manufacturing variations in the differential amplifier 6, an extra voltage, a DC offset, is added to the input side of the differential amplifier 6. This adds a DC offset component to the output voltage Vop of the differential amplifier 6. Therefore, the average of the inverted first output signal and the second output signal is calculated. This makes it possible to cancel the DC offset component. This improves the accuracy of measuring the temperature of the object.

[0026] Embodiment 3 11 is a plan view showing an imaging device according to embodiment 3. A first switch 11a connects the first hollow pixel 3a and the second hollow pixel 3b to one of the first input terminal IN1 and the second input terminal IN2. A second switch 11b connects the first non-hollow reference pixel 4a and the second non-hollow reference pixel 4b to the other of the first input terminal IN1 and the second input terminal IN2.

[0027] By switching the first switch 11a and the second switch 11b, the differential amplifier 6 receives the output voltage of the first hollow pixel 3a through the first input terminal IN1 and the output voltage of the first non-hollow reference pixel 4a through the second input terminal IN2, and outputs a first output signal. By switching the first switch 11a and the second switch 11b, the differential amplifier 6 receives the output voltage of the second hollow pixel 3b through the second input terminal IN2 and the output voltage of the second non-hollow reference pixel 4b through the first input terminal IN1, and outputs a second output signal. The inverting and averaging circuit 10 calculates the average of the inverted first output signal and the second output signal. This achieves the same effects as in the second embodiment.

[0028] Embodiment 4 FIG. 12 is a circuit diagram showing an imaging device according to a fourth embodiment. The output voltages of the hollow reference pixel 3′ and the non-hollow reference pixel 4′ arranged in the light-shielded region 12 are input to an operational amplifier 13. The hollow reference pixel 3′ has the same structure as the hollow pixel 3. The non-hollow reference pixel 4′ has the same structure as the non-hollow reference pixel 4. A current source 5 supplies a reference bias current Ibias1 to the hollow reference pixel 3′. The output of the operational amplifier 13 is input to a transistor 14 of the current source 5 to control a bias current Ibias2 of the non-hollow reference pixel 4′. That is, the current source 5 controls the bias current Ibias2 according to the output of the operational amplifier 13 so that the output voltages of the hollow reference pixel 3′ and the non-hollow reference pixel 4′ arranged in the light-shielded region 12 are the same (see FIG. 7). Note that the bias current Ibias1 may be controlled according to the output of the operational amplifier 13, using the bias current Ibias2 as a reference.

[0029] Currents that are the same as or proportional to the hollow reference pixels 3' and non-hollow reference pixels 4' in the shaded region 12 are passed through the hollow pixels 3 and non-hollow reference pixels 4 in the unshaded pixel array portion, respectively, by a current mirror or the like. This reduces the potential difference input to the differential amplifier 6, thereby preventing saturation of the differential amplifier 6. The other configurations and effects are the same as those of the first embodiment.

[0030] Embodiment 5. 13 is a plan view showing an imaging device according to embodiment 5. In this embodiment, the hollow pixels 3 and non-hollow reference pixels 4 in the even-numbered columns of embodiment 1 are swapped, and the hollow pixels 3 and non-hollow reference pixels 4 in the adjacent odd-numbered columns are shared. That is, in the configuration of embodiment 1, the non-hollow reference pixels 4 are shared between adjacent pixels 2. This reduces the area occupied by the non-hollow reference pixels 4 in each pixel 2, allowing the area of ​​the hollow pixels 3 to be expanded.

[0031] 14 is a plan view showing a modified example of the imaging device according to Embodiment 5. In the configuration of Embodiment 2, adjacent pixels 2 share a non-hollow reference pixel 4. This reduces the area occupied by the non-hollow reference pixel 4 in each pixel 2, thereby increasing the area of ​​the hollow pixel 3. [Explanation of symbols]

[0032] REFERENCE SIGNS LIST 1 semiconductor chip, 2 pixel, 2a first region, 2b second region, 3 hollow pixel, 3a first hollow pixel, 3b second hollow pixel, 4 non-hollow reference pixel, 4a first non-hollow reference pixel, 4b second non-hollow reference pixel, 5 current source, 6 differential amplifier, 10 inverting averaging circuit, 11a first switch, 11b second switch, 13 operational amplifier, IN1 first input terminal, IN2 second input terminal

Claims

1. A semiconductor chip, a plurality of pixels formed in a matrix on the semiconductor chip, a differential amplifier, and a current source, each pixel having a hollow pixel and a non-hollow reference pixel adjacent to each other, the differential amplifier amplifying an output voltage difference between the adjacent hollow pixel and the non-hollow reference pixel, the current source supplying a bias current to the hollow pixel and the non-hollow reference pixel, the current source being characterized in that the bias current of the non-hollow reference pixel is made lower than the bias current of the hollow pixel so that an output voltage difference between the hollow pixel and the non-hollow reference pixel in a state where no infrared ray is incident becomes small. An imaging device.

2. A semiconductor chip, a plurality of pixels formed in a matrix on the semiconductor chip, a differential amplifier, and an inversion averaging circuit connected to a subsequent stage of the differential amplifier, each pixel having a hollow pixel and a non-hollow reference pixel adjacent to each other, the differential amplifier amplifying an output voltage difference between the adjacent hollow pixel and the non-hollow reference pixel, the hollow pixel having a first hollow pixel and a second hollow pixel, the non-hollow reference pixel having a first non-hollow reference pixel adjacent to the first hollow pixel and a second non-hollow reference pixel adjacent to the second hollow pixel, the differential amplifier having a first input terminal and a second input terminal, the differential amplifier inputting the output voltage of the first hollow pixel from the first input terminal and inputting the output voltage of the first non-hollow reference pixel from the second input terminal to output a first output signal, the differential amplifier inputting the output voltage of the second hollow pixel from the second input terminal and inputting the output voltage of the second non-hollow reference pixel from the first input terminal to output a second output signal, the inversion averaging circuit being characterized in that it obtains an average of the inverted first output signal and the second output signal. An imaging device.

3. Each pixel is divided into first and second regions, the first hollow pixel and the first non-hollow reference pixel are formed in the first region, the second hollow pixel and the second non-hollow reference pixel are formed in the second region in an arrangement order opposite to that of the first hollow pixel and the first non-hollow reference pixel, the first hollow pixel and the second non-hollow reference pixel are connected to the first input terminal, The imaging device according to claim 2, wherein the second hollow pixel and the first non-hollow reference pixel are connected to the second input terminal.

4. A first switch that connects the first hollow pixel and the second hollow pixel to one of the first input terminal and the second input terminal; The imaging device according to claim 2, further comprising a second switch that connects the first non-hollow reference pixel and the second non-hollow reference pixel to the other of the first input terminal and the second input terminal.

5. An operational amplifier that inputs the output voltages of the hollow reference pixel and the non-hollow reference pixel disposed in the light-shielded region, respectively; The imaging device according to claim 1, wherein the current source controls a bias current of the hollow pixel or a bias current of the non-hollow reference pixel according to an output of the operational amplifier.

6. The hollow pixel is thermally insulated from the semiconductor chip, The imaging device according to any one of claims 1 to 5, wherein the non-hollow reference pixel is thermally connected to the semiconductor chip.

7. The imaging device according to claim 6, wherein the non-hollow reference pixel has the same diode structure as the hollow pixel.

8. The imaging device according to any one of claims 1 to 5, wherein the non-hollow reference pixel is shared by adjacent pixels.

Images