JPH06204573A - Pyroelectric solid-state imaging device - Google Patents

Abstract

PURPOSE:To reduce the rate of using an Al layer, the first layer, as an interconnection without increasing the number of layers of polycrystalline silicon by wiring a connection gate and reset gates with one wiring and by setting threshold voltage of the reset gates larger than that of the connection gate. CONSTITUTION:Three gates, reset gates RG1, RG2 and a connection gate CG, are so connected to each other that they may be controlled by one terminal TG. By setting voltage to be applied to the TG when the voltage of diodes D1, D2 is set at Vinit at a different level from that when a signal is read out on a CCD from the diode D1, D2, the number of wirings of a picture element section can be reduced from 4 to 1. In this way, the complexity of a wiring pattern of the picture element section is reduced and thereby additional plane space is generated. Therefore, an yield can be increased in building a device. Moreover, an area of a pyroelectric film can be increased and then a numerical aperture and a sensitivity can be increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device, and more particularly to a solid-state image pickup device for picking up an infrared image.

[0002]

2. Description of the Related Art A pyroelectric infrared sensor is a visible light sensor.
Optics using infrared optical materials such as Ge
An infrared image is formed using a lens. Infrared is heat
Is absorbed by the pyroelectric film, and the film surface has a temperature corresponding to the infrared image.
Degree change distribution occurs. The polarization of the pyroelectric film increases with temperature
The pyroelectric effect reduces the temperature change distribution in the film.
Is converted to the surface charge distribution. Pyroelectric effect is dielectric time
It is due to the dynamic temperature change.
A chord that temporally interrupts infrared light on the front surface of the solid-state image sensor.
It is necessary to provide a par. By the temporal interruption of infrared light
When the temperature of the pyroelectric film changes by ΔT, the pyroelectric coefficient P _TWhen
Then, the amount of charge ΔQ induced on the film surface is P_T・ △ T.
△ Q is due to the increase or decrease of polarization, so both sides of the pyroelectric film
The absolute value of the amount of electric charge induced in is equal and the sign is opposite.
FIG. 5 shows a conventional pyroelectric solid-state image pickup device for picking up an infrared image.
3 is a diagram equivalently showing the pixel portion of FIG. The pyroelectric element is a
Sensor C and current source I_SIs represented by. Pyroelectric element
In order to short-circuit both ends to the initial voltage Vinit,
Set transistors MR1 and MR2 are connected
It A diode D1 that integrates a signal as a capacitive element,
The charge accumulated in D2 is the read transistor MY1,
The gates YG1 and YG2 of MY2 are controlled to pass through the coupling section.
Are transferred to the CCD. 20-1 and 20-2 are CCD
Indicates the transfer unit. Figure 6 (a) shows one end of the pyroelectric element
Connected reset transistor MR1, diode
D1, read transistor MY1, coupling part MC, CC
It is sectional drawing along D. FIG. 6B shows another example of the pyroelectric element.
It is sectional drawing about the same structure about one end. This
In the conventional example as described above, the signal is read from the pyroelectric element.
In addition, each pixel has a two-system signal transfer mechanism. 1
Is p-type semiconductor substrate, 2 is n-type diffusion for CCD channel
Layer 3-1 is n for reset / drain RD which also serves as wiring
+ Type diffusion layer, 3-3 is a signal connected to the lower surface of the pyroelectric film 12
N + type diffusion layer for forming the integrating diode D1, 3-4 is a focus layer
Forming a signal integrating diode D2 connected to the upper surface of the electric film 12
It is an n + type diffusion layer for. 4-1 and 4-2 are focal points
The lower and upper surfaces of the electric film 12 are set to the initial voltage Vinit
Reset transistors MR1 and MR2
P-type diffusion layers for channels, 9-1 and 9-2 are MR
1. MR2 gate electrode. 5 is a channel stopper
P + type diffusion layer, 6 for insulation isolation S_iD₂, 8-1, 8-
2 sets D1 and D2 to the read voltage Vread, respectively.
Read gates YG1, YG2, and 21 for determining
Combine the two signal flows from the iodines D1 and D2 into one.
Combined gate C for stopping and transferring to CCD channel 2
G, and a little with YG1, YG2 and CCD gate 7
It is a Y-shaped gate electrode having an overlap. 11-4,
11-5 is the first layer connected to YG1 and YG2, respectively
Al layers, 10 and 14 are S_iO₂Or polyimide
Interlayer insulating film such as, 13 is a heat absorbing film such as nichrome, 1
Reference numeral 5 is a second Al layer for wiring and light shielding. Figure 7
8 is a pulse timing diagram for explaining the operation of the conventional example, FIG.
7A and 7B show time t in FIG.₁~ T_Five6 in
A surface potential corresponding to (a) and (b).
It The shaded area shows that it is full of electrons.
Below, open the chopper and apply incident infrared light to the device surface to pyroelectrically
When the temperature of the film rises, the pyroelectric effect of the pyroelectric film 12 is caused by the pyroelectric effect.
Only when polarization is applied so that negative charges are induced on the bottom surface.
The operation will be described. Time t in FIG.₁As shown in
During the vertical blanking period (V-BLK), the chopper opens.
The voltage V is applied to the reset gate (RG) while changing to the normal state.
_GHIs applied to turn on MR1 and MR2, and the pyroelectric film 1
Both sides of 2 are short-circuited and the voltage is set to Vinit. R
Voltage V on G_GLIs applied to turn off MR1 and MR2.
Then, the channels under the gates of YG1 and YG2 are turned off.
Since it is in the status
Signal integration is started in the signal integration diodes D1 and D2.
It As the temperature rises, the lower surface of the pyroelectric film has a negative charge and the upper surface has a positive charge.
Since the load is induced, time t in FIG.₂Then, as shown in Figure 8, D
The potential of 1 decreases and the potential of D2 increases. Time t₃so
YG to transfer charge from D1 to CCD 20-1
1, V for each CG_YH, V_CHAnd apply the
Open the channel. The charge amount Qread at this time is Vinit
And the amount of bias charge Qbias determined by Vread
And the amount of charge Qsig induced on the lower surface of the pyroelectric film 12
Becomes Qbias + Qsig. Vread is a gate mark
Applied voltage V_YHAnd the threshold voltage of YG1. From D1
Charge transfer is completed (the diode voltage is Vread
Becomes V), and V in YG1 and CG respectively_YL, V_CLApply
And close the channel under the gate. At this time, the charge Qre
ad is stored in CCD 20-1 in FIG. 5, but C
The CD is driven and shifted by 1 bit, and the next CCD is transferred.
It is moved to the sending unit 20-2. Time t_FourThen YG2, C
Open the G channel and connect the diode D2 to CCD20-1.
Transfer charge to. The charge amount Q'read at this time is the pyroelectric
Qbias due to the amount of charge Q'sig induced on the upper surface of the film
-Q'sig. Closed YG2 and CG channels
After time t_FiveThen time t₁Turn on MR1 and MR2 in the same manner as
State and set the voltage of diodes D1 and D2 to Vinit
Reset. When the chopper is closed to block infrared light, pyroelectric
Since the temperature of the film decreases, the charge of the opposite sign
Is induced. During this signal charge integration, transfer to CCD first
The charged charges are sequentially scanned and taken out from the image sensor.
The external circuit detects this amount of charge and opens the chopper during the open period.
Readout including signals Qsig and Q'sig stored in
For the electric charge, Qread-Q 'for each unit pixel
For read and vice versa, Q'read-Qr
By performing the ead, the bias charge Qbias is canceled.
The signal Qsig output from the unit pixel after canceling
You can get + Q'sig.

[0003]

In this conventional example, RG, YG1, Y are used as the gate wiring of the pixel portion in addition to the CCD gate.
Four G2 and CG are required. The CCD gate is formed on the lattice in the pixel portion, and is usually formed by the first and second polycrystalline silicon layers. Therefore, these four wires are to be wired in the third and subsequent polycrystalline silicon layers or in the first Al layer. However, as the ratio of using the first Al layer as a wiring increases, the area of the pyroelectric film decreases and the infrared sensitivity decreases. Further, when the number of layers of polycrystalline silicon is increased, the yield is reduced due to the increase in the number of manufacturing processes. An object of the present invention is to reduce the ratio of using the first Al layer as a wiring without increasing the number of polycrystalline silicon layers.

[0004]

In order to achieve the above-mentioned object, the present invention shares the wiring of the coupling gate CG and the reset gate RG by one wiring, and sets the threshold voltage of the reset gate to the threshold of the coupling gate. It is larger than the value voltage.

[0005]

As a result, even if the coupling gate is on, the signal can be read out while the reset gate is off, and the number of gate wirings in the pixel portion is reduced from four to three. The ratio of using the first Al layer as a wiring can be reduced without increasing the number of layers of polycrystalline silicon, and the aperture ratio and sensitivity can be improved.

[0006]

EXAMPLES The present invention will be described below with reference to examples. FIG. 1 is a diagram equivalently showing a pixel portion of a pyroelectric solid-state imaging device of the present invention. This imaging device has two systems of signal transfer mechanism for transferring the signal charges induced on both sides of the pyroelectric film to the CCD. FIGS. 2A and 2B are cross-sectional views of the respective paths. is there. As shown in FIG. 1, in the image pickup device of the present invention, three gates of reset gates RG1 and RG2 and a coupling gate CG are connected so as to be controlled by one terminal TG. Set the voltage of the diodes D1 and D2 to Vinit
And the voltage applied to TG when set to
By setting the value of the voltage applied to the TG when reading the signal from the D1 and D2 to the CCD to a different value, the wiring of the pixel portion is
I have reduced it from one to one. 20-1, 20-2, 20
-3 is a CCD transfer unit. 23-1, 23 in FIG.
-2 is a P-type diffusion layer for controlling the threshold voltage of the transistors MY1, MY2, MC. Especially, the threshold voltage of MC is a transistor MR1, in consideration of the n-type diffusion layer of the CCD channel 2. It becomes lower than the threshold voltage of MR2. Reference numerals 22-1 and 22-2 denote wiring portions of the gate 8-1 of the transistor MY1 and the gate 8-2 of the transistor MY2, respectively, which are formed of the third-layer polycrystalline silicon. FIG. 3 is a pulse timing diagram for explaining the driving method of the present invention, FIG.
FIG. 2B is a diagram of FIGS. 2A and 2B at times ta to te of FIG.
Are surface potentials corresponding to. The shaded area in FIG. 4 indicates that it is full of electrons. Below is a description of the case where polarization processing is performed so that the negative electric charge is induced on the lower surface of the pyroelectric film by the pyroelectric effect when the temperature of the pyroelectric film rises by opening the chopper and applying incident infrared light to the element surface. The operation will be described. As shown at time ta in FIG. 3, while the chopper changes to the open state in the vertical blanking period (V-BLK), the voltage V _GH is applied to the reset gate RG to turn on the reset transistors MR1 and MR2. , Both sides of the pyroelectric film are short-circuited and the voltage is set to Vinit.
Next, the voltage V _GL is applied to RG to turn off MR1 and MR2.
When brought into the state, the diodes D1 and D2 are brought into a floating state and the integration of signals is started. Since negative charges are induced on the lower surface of the pyroelectric film and positive charges are induced on the upper surface of the pyroelectric film due to the temperature increase, the potential of D1 decreases and the potential of D2 increases at time tb in FIG. 3 as shown in FIG. At time tc, V is applied to YG1 and TG, respectively.
_YH and V _TM are applied to open the channel, D1 to CCD2
The charge is read to 0-1. Here, V _TM is a voltage at which the reset transistors MR1 and MR2 do not turn on, and CG
The potential under the gate of is set to be lower than YG1. This is because if the reset transistors MR1 and MR2 are turned on, charges will flow from the reset drain RD. Read voltage Vread is YG
The charge amount Qread to be read at this time is the sum Qbias + Qsig of the bias charge amount Qbias determined by Vinit and Vread and the charge amount Qsig induced on the lower surface of the pyroelectric film. Here, Vread is determined by the voltage V _YH applied to YG1 and the threshold voltage of the transistor MY1. Diode D
When the voltage of 1 becomes Vread and the charge transfer ends, YG
The channels are closed by applying V _YL and V _TL to 1 and TG, respectively. Then, drive the CCD to shift by 1 bit,
The charge Qread accumulated in the CCD 20-1 of FIG. 1 is moved to the next transfer unit. Next, at time td, YG2 and TG
Each application of V _YH, V _TH to open the channel, transfers the charge from the diode D2 to CCD20-1. The charge amount Q′read at this time becomes Qbias−Q′sig due to the charge amount Q′sig induced on the upper surface of the pyroelectric film. After the transfer is completed, V _YL and V _TL are applied to YG2 and TG, respectively, to close the channel, and at time te, D1 and
Reset D2 to Vinit. When the chopper is closed to block the infrared light, the temperature of the pyroelectric film is lowered, so that the electric charge of the opposite sign is induced. During this signal integration, the charge previously transferred to the CCD is transferred from the CCD 20-2 to the CCD.
20-3 to CCD 20-1 CCD just opened
Charges are sequentially scanned to 20-2 and taken out from the image sensor.

[0007]

As described above, in the past, four gate wirings RG, YG1, YG2, and CG were required as the gate wiring of the pixel portion, whereas in the present invention, the wirings of RG and CG are shared. As a result, the number of wiring patterns is reduced to three, the complexity of the wiring pattern of the pixel portion is reduced, and a planar allowance is provided, so that the yield in terms of device configuration is improved. Moreover, since the proportion of the first Al layer used as the wiring is reduced, the area of the pyroelectric film can be increased, and the aperture ratio and the sensitivity can be improved. Since the proportion of using the first Al layer as a wiring is reduced without increasing the number of layers of polycrystalline silicon, there is no reduction in yield that would be caused by an increase in the number of manufacturing process steps.

[Brief description of drawings]

FIG. 1 is an equivalent diagram of a pixel portion of a pyroelectric solid-state imaging device of the present invention.

FIG. 2 is a sectional view of a pyroelectric solid-state imaging device according to the present invention.

FIG. 3 is a pulse timing chart for explaining the operation of the present invention.

FIG. 4 is a surface potential diagram for explaining the operation of the present invention.

FIG. 5 is an equivalent diagram showing an example of a conventional solid-state imaging device.

FIG. 6 is a sectional view of a conventional example.

FIG. 7 is a pulse timing chart of a conventional example.

FIG. 8 is a surface potential diagram of a conventional example.

[Explanation of symbols]

 RG1, RG2 reset gate CG coupling gate D1, D2 diode

Claims (1)

[Claims] A photoelectric device including a pyroelectric element formed of a dielectric material showing pyroelectricity on the main surface of a semiconductor substrate of the first conductivity type, and a capacitive element for separately accumulating charges induced on the upper surface and the lower surface of the pyroelectric film. A conversion element is formed, an initial voltage setting element and a read voltage setting gate are provided for each capacitance element, and each read voltage setting gate and a signal are transferred to transfer the charge accumulated in each capacitance element to the signal charge transfer element. In a pyroelectric solid-state imaging device in which a coupling gate is provided to be connected to a charge transfer element and each of which is a unit, and which is formed in an array, the control gate and the coupling gate of the initial voltage setting element can be controlled by the same terminal. And a threshold voltage of the control gate higher than a threshold voltage of the coupling gate.