JPH02230769A - Pyroelectric type solid-state image sensing device - Google Patents

Abstract

PURPOSE:To improve dynamic range and S/N ratio by a method wherein electric charge induced on the upper surface of a pyroelectric film is utilized as a signal by storing electric charge induced on the upper surface and the lower surface of the pyroelectric film of a pyroelectric type solid state image sensing device, in different capacitance elements. CONSTITUTION:A p-type diffusion layer 4-2 for the channel of a second reset transistor MR-2 for setting the upper surface of a pyroelectric film 12 connected through an Al layer 11-3 of a first layer and an Al layer 15 of a second layer at an initial voltage Vinit, and an n<+> type diffusion layer 3-3 as a capacitor for integrating a signal induced on the pyroelectric film 12 are provided. An n<+> type diffusion layer 2-4 for the channel of a buried type CCD for transferring the signal induced on the upper surface of the pyroelectric film 12 is formed, and the signal is led out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a solid-state imaging device, and particularly to a solid-state imaging device that captures infrared images.

[Summary of the invention]

The present invention uses a CCD solid-state imaging device that obtains infrared images to store the charges generated on the upper surface and the lower surface of the pyroelectric film of the device in separate capacitive elements and read them out. It is an improved version. In other words, in conventional pyroelectric solid-state imaging devices, the charge induced on the top surface of the pyroelectric film is discarded because the wiring is connected to an external power supply, and the charge induced by the pyroelectric effect cannot be used effectively. The drawback is that it cannot be used.

An object of the present invention is to provide a pyroelectric solid-state imaging device that makes full use of the charges induced by the pyroelectric effect and can easily remove bias charges.

The present invention is characterized in that charges induced on the lower surface and upper surface of the pyroelectric film of a pyroelectric solid-state imaging device are stored in separate capacitive elements, and for each capacitive element, an initial voltage setting element and an initial voltage setting element of the capacitive element are stored. Each device is provided with a transfer element that transfers charge from the capacitive element to the CCD.

As a result, according to the present invention, whereas conventionally only the charge induced on the lower surface of the pyroelectric film was treated as a signal and the charge induced on the upper surface of the pyroelectric film was discarded, according to the present invention, the upper and lower Since the charges on both sides can be treated as signals, the dynamic range and S/N ratio can be greatly improved. In addition, since the bias charge injected for each pixel can be easily removed by taking the difference between the signals on the top and bottom surfaces of the pyroelectric film in each pixel, fixed patterns caused by variations in the bias charge in each pixel can be easily removed. Noise can be suppressed.

[Conventional technology]

Unlike visible light sensors, pyroelectric infrared sensors
An infrared image is formed using an optical lens using an infrared optical material such as e. Infrared rays are absorbed as heat by the pyroelectric film, creating a temperature change distribution on the film surface that corresponds to the infrared image. Since the polarization of the pyroelectric film decreases with increasing temperature,
The pyroelectric effect converts the temperature change distribution into the surface charge distribution of the film. Since the pyroelectric effect is caused by temperature changes over time in a dielectric material, it is necessary to provide a cyonopa in front of the solid-state image sensor to intermittent infrared light in order to image a stationary object. The temperature of the pyroelectric film increases by Δ due to the temporal interruption of infrared light.
When the amount of change is T, the amount of charge ΔQ induced on the film surface becomes PT·ΔT, where PT is the pyroelectric coefficient. Since ΔQ is due to an increase or decrease in polarization, the absolute values of the charge waves induced on both sides of the pyroelectric film are equal (<<, but the signs are opposite).

Figure 7 is a cross-sectional view of a conventional infrared image sensor that captures infrared images, and Figures 8 (a) and 8 (b) correspond to Figure 7 when reading signals in different imaging striations. The shaded area is filled with electrons. FIG. 9 is an equivalent circuit corresponding to FIG. 7 when a four-phase drive type vertical CCD is used. In the figure, 1 is a P-type semiconductor substrate, 2-1 is an embedded CCD
2-2 is the n-type diffusion layer for the channel of the transfer gate, 3-1 is the recenote drain (
The n-type diffusion layer 3-2 for
type diffusion layer, 4 is P for the channel of the resenoto transistor
5 is a P-type diffusion layer for channel stopper, 6 is Si02 for insulation isolation, 7-1 is the first layer of polycrystalline silicon, and as shown in FIG. A CCD electrode is constituted by the crystalline silicon 7-1 and a second layer of polycrystalline silicon 7-2 which slightly overlaps with each other. 8 is a transfer gate (TG) for transferring signal charges to the CCD channel.
) and 9 are gate electrodes (RG) of reset transistors for initial voltage setting, and are each made of third layer polycrystalline silicon. 11-1 is the first eyelet Ae layer for wiring of the reset drain 3-1, 11-2 is the first eyelet Ag layer for the pyroelectric film electrode, 12 is the pyroelectric film, and the pyroelectric film 12 is shown in FIG. is equivalently shown by a capacitor and a current source. 1
3 is a heat absorption film such as nichrome, 10 and 14 are SIO2
Alternatively, an interlayer insulating film such as polyimide, 15 is a second Ae layer for wiring and light shielding, 16 & is an external power supply, and a bias voltage Vini is applied to the reset drain 3-1.
Apply t. 17 is a signal integrating diode.

FIG. 10 shows the timing of the opening/closing of the Chosopar which intermittent infrared light and the driving pulse for explaining the operation of the pyroelectric solid-state imaging device of this conventional example. When the chopper is opened and incident infrared light is applied to the element surface, the pyroelectric film 12 is caused by the pyroelectric effect.
The operation will be described in the case where polarization treatment is performed to induce negative charges (electrons) on the Ae layer 11-2 side. 10th
As shown at time t1 in the figure, when the channel is closed, the voltage Vn is applied to the transfer gate (TG) 8 to cut off the transfer channel 2-2, and the transfer gate (RG) is cut off.
) Voltage V at 9. By applying M and turning on the reset transistor, both sides of the pyroelectric film 12 are short-circuited. Since Vinit is applied to the drain (RD) 3-1 regardless of whether the chopper is opened or closed, the voltage on both sides of the pyroelectric film 12 is also Vinit. Next, when you open the chonopa, the voltage vG will be applied to RG (RG) 9.
Signal integration is started by applying L to turn off the reset transistor and put the signal integration diode 17 into the 7 loading state. Due to the pyroelectric effect caused by the incident infrared light, some electrons are liberated on the i-layer 11-2 side of the pyroelectric film 12, and the positive charges induced on the heat absorption film 13 side, which are accumulated in the diode 17, are shown in FIG. As described above, electrons are supplied from the external power source 16 and neutralized. When reading a signal, a voltage vT{ is applied to the transfer gate 8 as shown at time t2 in FIG.
is applied, and the potential of the transfer channel 2-2, V r e a
Set to d. The surface potential at this time is shown in FIG. 8(a). Diode 17 to CCD channel 2-
The charge Qread transferred to Vread 1 is the sum of the charge Qsig caused by the pyroelectric effect and a certain amount of bias charge Qbias corresponding to the potential difference between Vread and Vinit. Therefore, it is sufficient to subtract an amount corresponding to the charge Qbias injected by the signal processing circuit.

Contrary to the above, when the chopper is opened, A of the pyroelectric film 12
If polarization treatment is performed to induce positive charges on the l layer 11-2 side, the opening/closing of the chonoper and the drive pulse timing can remain as shown in Figure 10, but the surface potential during signal readout will be as shown in Figure 8 (b). )become that way. This is because the polarity of the induced charges is reversed, so the way the charges are neutralized is different.

In this case, the transfer charge Qread is the bias charge Qb i
Since it is the difference between as and the signal charge Qsig, the signal can be detected by subtraction in the signal processing circuit.

The structure and driving method of such a pyroelectric solid-state imaging device are described in, for example, Japanese Utility Model Application No. 138220/1983.

[Invention or problem to be solved]

In the pyroelectric solid-state imaging device of this conventional example, by injecting a fixed amount of bias charge every time when reading a signal, regardless of whether the charge induced on the lower surface of the diaphragm 12, that is, on the side of the Al layer 11-2, is positive or negative, Although it has the advantage that the electric charge can be treated as a signal, as can be seen from FIG. Therefore, there is a drawback that the charge induced by the pyroelectric effect cannot be used effectively.Also, if there is variation in the injected bias charge Qbias, the Qbias cannot be effectively removed by an external circuit. be.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focused solid-state imaging device that makes full use of the charges induced by the pyroelectric effect and can easily remove bias charges.

[Means to solve the problem]

In order to achieve the above object, the present invention accumulates charges induced on the lower surface and upper surface of the pyroelectric film 12 of a pyroelectric solid-state imaging device in separate capacitive elements, and A transfer transmitter is provided for transferring charge from the voltage setting element and the capacitive element to the CCD.

[Effect]

As a result, the charge induced on the top surface of the focal film, which was conventionally discarded, can now be used as a signal, making it possible to significantly improve the dynamic range and S/N ratio. Furthermore, the injected bias charge for each pixel can be removed by taking the difference between the signals on the top and bottom surfaces of the pyroelectric film in each pixel, so fixed pattern noise caused by variations in the bias charge in each pixel can be suppressed.

〔Example〕

The present invention will be explained below using examples.

FIG. 1 is a cross-sectional view of the pixel part of the pyroelectric solid-state imaging device of the present invention.
Figure 2 shows the corresponding surface potential, and the shaded area shows that it is filled with electrons. 4-1 is a P-type diffusion J* for the channel of the first recenote transistor (MRI) for setting the lower surface of the pyro-t film 12 connected to the i-wire 11-2 to the initial voltage Vinit. , 9-1 is the MRI gate electrode 0
4-2 is the first layer 1' layer 11-3 and the second layer Al+
9-2 is the gate electrode of MR2; 9-2 is the gate electrode of MR2; 3 is jiao"j::'qi&,1
2 is induced on the top surface. 02-4 is an n-type diffusion layer as an integral quantity of a signal, and 2-3 is an n-type diffusion layer for a channel of an embedded CCD for transferring a signal induced on the upper surface of the pyroelectric film 12. This is the gate channel. 8-
1.8-2 are gate electrodes for transferring charge to the COD, and 17-1.17-2 in FIG. 3 are signal integrating diodes. Here, as shown in Figure 3, MHI, MR
The second gate electrodes 9-1 and 9-2 are reset gate electrodes 9-1 and 9-2, respectively.
} (RG) terminal, and the gate electrodes 8-1 and 8-2 are each connected to a transfer gate (TG) terminal.

FIG. 4 is a timing diagram of the opening and closing of the chopper and the pulses for driving the imaging device, for explaining the operation of the pyroelectric fixed imaging device of the present invention. When the chopper was opened and incident infrared light was applied to the element surface and the temperature of the pyroelectric film rose, polarization treatment was performed so that negative charges (t-sons) were induced on the lower surface of the pyroelectric film 12 by the pyroelectric effect. The operation will be explained for each case.

As shown at time ta in Figure 4, the vertical blanking period is open (・
During the transition to the reset state, the voltage VG is applied to the reset gate (RG').
}Apply I to reset transistors MRl, MR2
is turned ON, both sides of the pyroelectric film 12 are short-circuited, and the voltage V
Cent to init. Next, reset gate (RG
) by applying voltage VGL to the recent transistor M
Turn RI and MR2 off. Transfer gate (TG)
is off (t pressure VTL is applied), and the signal integration diodes 17-1, 17-2 are in a floating state, so signal integration is started. Since negative charges are induced on the bottom surface of the pyroelectric film 12 and positive charges are induced on the top surface, the diode 17-1
(If <<, the potential of the diffusion layer 3-2) decreases, and the potential of the diode 17-2 (or the diffusion layer 3-3) increases.

Transfer cell (T
G) is turned on (t pressure VTH is applied and the accumulated charge is read out. The surface potential corresponding to Fig. 1 at this time is shown in Fig. 2. The charge Qrea transferred to the CCD channel 2-1
d is Qbias+Qsig, C C D channel 2
Charge transferred to −4 Amount of charge induced on the lower surface of the pyroelectric film 12 + Q”ig is an amount of charge induced on the upper surface of the pyroelectric film, Qb
ias is the initial voltage Vinit of the diode 17-1.17-2 and the transfer channel 2-2.
This is the bias charge amount determined by the voltage Vread of 2-3. Vread is determined by the voltage VTH applied to the transfer gate (tG). Diode 17-1.17-2
The charge transfer from the diode 17-1.17 is completed.
-2 voltage becomes Vread), the transfer gate is turned off.

Next, the reset transistors MHI and MR2 are turned on, and the diodes 17-1 and 17-2 are set to the initial voltage V again.
Set to init. The chopper is closed, reset transistors MHI and MR2 are turned off, and signal accumulation begins. At this time, the chopper closes to block infrared light, so the temperature of the pyroelectric film 12 decreases, and a charge opposite to that of the previous 7 fields is induced. That is, negative charges are induced on the upper surface of the pyroelectric ml2, and positive charges are induced on the lower surface K. The surface potential when the transfer gate is turned on again at time tc is
This is a left-right inverted version of Fig. 2, which shows the surface potential on b. That is, the charge Qread transferred to the CCD channel 2-1 is Qbias-Qsig, CCD
The charge Qread transferred to channels 2-4 is Qb i
as -4- Q's ig to7'. Cru. As described above, according to the present invention, the pyroelectric film 12
It becomes possible to take out the charges generated on the top surface and the charges generated on the bottom surface.

The absolute values of the charges generated on the top and bottom surfaces of the pyroelectric film 12 are equal.
, the sign is opposite. Therefore, to remove the bias charge Qbias superimposed on the signal, Qread − Qr
If ead or Qread - Q,read is performed, Qsig + Qsig is obtained. FIG. 5 is a block diagram showing an example of a signal processing circuit of a pyroelectric solid-state image sensor according to the present invention. 101 is a pyroelectric solid-state image sensor, 10
2 is a drive circuit for the image sensor, 103 is a amplifier, 10
4 is a subtraction circuit that outputs the difference between preamplifier outputs P and Q;
105 and 106 are separation circuits using analog switches, etc., 107 is a polarity reversal circuit, 108 is an infrared lens made of Ge, etc., 109 is a chopper that temporally interrupts infrared light, 110
is a control circuit that controls the opening and closing of the chopper and the operation of the separation circuit.

FIG. 4 shows the timing of the control signals CHOP.1 and CHOP.2 output from the control circuit 110 together with other drive pulses. Figure 6(a) is P of Figure 5.
This is the waveform at CCD channel 2-1.
It is shown to correspond to the charge Qread transferred by . Similarly, it corresponds to the charge Q read transferred by the CCD channel 2-4. The charges accumulated during the period when the chopper is open are sequentially output from the image sensor together with the bias charge Qbias during the period when the chopper is closed. The waveform when the chopper is closed is shown in the left half of Figure 6, and the waveform when the chopper is open is shown in the right half of Figure 5. The two signal lines output from the image sensor 101 each pass through a pre-amplifier 103, and the waveform at point R in FIG. 5, which is the output of the zero subtraction circuit 104, is input to the subtraction circuit 104 as shown in FIG. 6(C). It becomes like this. In this way, the implanted particles can be removed for each pixel. Next, as shown in FIG. 4, the control circuit 110 inputs sampling pulses CHOP-1 and CHOP-2 synchronized with the opening and closing of the chopper to separation circuits 105 and 106, respectively, to select the signal flow path. . CHOP・1 during the period when the chopper is closed
is set to lOW level vCL, CHOP・2 to high level VC}I to shut off the separation circuit 105, and the signal passes through the separation circuit 106.0 Also, during the period when the chopper is open, CHOP・1 is set to VCH, CHOP・2 Since the signal is set to VCL to cut off the separation circuit 106 and the signal passes through the separation circuit 105 and enters the inversion circuit 107, the waveform at point S in FIG. 5 becomes as shown in FIG. 6(d). Furthermore, if a synchronization signal is added through a low-pass filter, it can be treated as a video signal.

The present invention has been specifically explained above using examples, but
Modifications may be made within the scope of the spirit of the mourning.

For example, in FIG. 1, the second Al layer 15 connected to the top surface of the focal film 12 is connected to the first layer Aejso 11-3; The third layer of AI provided between 11-3 and the second Al layer 15! ! They may be connected through layers. In addition, for the wiring conductor, l, MOS}
We have explained the case where polycrystalline silicon is used for transistors and CCD gates, but Mo, W, Ti
, a high melting point metal such as Ta, or a silicide layer of the high melting point metal.

Furthermore, as shown in Fig. 1, elements such as an n-type CCD channel are formed on the main surface of a P-type semiconductor substrate, but a P-type semiconductor region is formed on the main surface of an n-type semiconductor substrate, and P
Elements such as n-type CCD channels may be formed in the type semiconductor region. All the conductivity types of the semiconductors may be reversed. Furthermore, the polarization of the pyroelectric film may be reversed. In FIG. 3, the gate electrodes of the reset transistors MRl, MR2 are combined into one terminal RG, but they may be separate terminals. The same applies to the terminal TG. The fourth is the same, but
The opening/closing period of the chonopa may be an integral multiple of the frame period. Further, the open period and the open period of the chopper may have different lengths.

Although the subtracter 104 is used in FIG. 5, it may be replaced by a differential amplifier that amplifies the difference between the signals at point P and point Q.

〔Effect of the invention〕

As explained above, in the past, only the charges induced on the bottom surface of the pyroelectric film were treated as signals, and the charges induced on the top surface of the pyroelectric film were discarded, but according to the present invention, the charges on the top, bottom, and both sides Since it can be treated as a signal, the dynamic range and S/N ratio can be greatly improved. In addition, the bias charge injected for each pixel can be easily removed by taking the difference between the signals on the top and bottom surfaces of the pyroelectric film in each pixel, suppressing fixed pattern noise caused by variations in the bias charge of each pixel. Can do 0

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of the pyroelectric solid-state imaging device of the present invention, and FIG. 2 is a surface potential diagram of the pyroelectric solid-state imaging device of the present invention.
FIG. 3 is an equivalent circuit diagram of a pyroelectric solid-state imaging device of the present invention, FIG. 4 is a pulse timing diagram of the present invention, and FIG. 5 is a cross-sectional diagram showing an example of a body imaging device according to an embodiment of the present invention. 8(t)(b)l are surface potential diagrams of a conventional solid-state imaging device, FIG. 9 is an equivalent circuit diagram of a conventional solid-state imaging device, and FIG. 10 is a pulse timing diagram in the conventional example. It is. 12 substrates, 3-1: reset train diffusion layer, 3-2.
3-3: Integral response diffusion layer, 4-1: First reset transistor for initial voltage setting, 4-2: Second reset transistor for initial voltage setting, 5: Channel stopper, 6:
Insulating separation layer, 8-1. 8-2: Gate electrode, 9
-1: MHI gate electrode, 9-2: MR2 gate electrode,
10: Insulating film, 11-1.11-2, 11-3: Al
Wiring, 12: Pyroelectric film, Fig. 2 Fig. 3/19 Fig. 4 Fig. 5 Fig. 6 ← Nara Noha o: P111 -Ra - ← Nayoppa Nikai 11 Fig. 8 Fig. 9 Figure 10

Claims (1)

[Claims] 1. A photoelectric conversion element consisting of a capacitive element group that stores optical information on the main surface of a semiconductor substrate of a first conductivity type, an initial voltage setting element for the capacitive element, and a pyroelectric element formed of a dielectric material exhibiting pyroelectricity. In a solid-state imaging device that integrates signal charge transfer elements that form a group and sequentially transfer signal charges accumulated in the capacitive element group, charges induced on the upper surface of a film of the pyroelectric element and the pyroelectric element Charges induced on the lower surface of the film are stored in separate capacitive elements, and each capacitive element is provided with an initial voltage setting element for the capacitive element and a transfer element for transferring charge from the capacitive element to a signal charge transfer element. A pyroelectric solid-state imaging device characterized by: