JP2605856B2 - Pyroelectric infrared imaging device and driving method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a configuration of a pyroelectric infrared imaging device using a solid-state scanning circuit, and an improvement in a driving method thereof.

FIG. 6 shows an equivalent circuit of a unit pixel for explaining a conventional signal readout method (signal current injection method) of a pyroelectric CCD (pyro CCD) in which a pyroelectric sensor is stacked on a CCD scanning circuit. FIG. 4 is a conceptual diagram of a driving potential. Positive and negative charges are generated in the pyroelectric sensor according to the opening and closing of the optical chopper. Si−
The CCD operates to read only one of the charges. Therefore, in the conventional example, half of the maximum transferable charge amount of the CCD is used as a bias charge and is electrically injected periodically with the opening and closing of the optical chopper so that input signal charges of both codes can be accepted. In FIG. 5, a pyroelectric sensor (pyro sensor) 10
The positive and negative signal charges 111 and 112 generated in 6 are read gate G
The data is transferred to the CCD scanning units GT ₁ (104) and GT ₂ (105) via R ₁ (103).

At this time, the input diode unit 101 is reset to the reset level 109 once in a cycle of opening and closing of the optical chopper, and then, while the bias charge 110 is electrically injected, the positive and negative electrodes of the pyrosensor Signal charges 111 and 112, and after a certain accumulation time, the gate
An operation of reading the data into the CCD scanning unit 102 via the GR ₁ (103) is performed. This is, for example, R. Watton, et al. Infrared Phys vol 2
2. PP.259-275 1982

Problems to be Solved by the Invention In the above-described conventional configuration, one accumulated signal is taken out to an external circuit as an infrared imaging signal in a fixed scanning cycle. Therefore, when an attempt is made to increase the density of pixels, difficulties arise in the following points.

(1) The spatial resolution of the infrared image is determined by the pyroelectric electrode gap of the pyroelectric sensor in the pixel section. Therefore, in the readout method of one accumulation signal, if the pyroelectric electrode gap becomes short due to the high density of pixels, thermal work occurs between pixels due to heat conduction within the accumulation time, and the spatial resolution of the infrared image Is caused.

(2) As the pixel density increases, the signal decreases and the SIN deteriorates. The present invention has been made in view of the above, and an object of the present invention is to provide a novel structure and a driving method for realizing a higher pixel count of a pyroelectric infrared imaging device.

Means for Solving the Problems The present invention uses the following means to solve the above problems. An injection diode for injecting a bias charge and a control gate are provided in a storage diode connected to a pyroelectric sensor in a pixel portion, and two control gates are formed for reading out signal charges from the storage diode to a scan line. Then, the optical chopper is opened and closed a plurality of times within one scanning period of a fixed cycle of the imaging system, and a bias charge is injected from the injection diode into the storage diode in synchronization with the opening and closing of the optical chopper. Next, in synchronization with the opening and closing of the optical chopper, the signal charges and the injection bias charges stored in the storage diode are alternately transferred to the storage area in the vertical scanning line via each control gate, Integrate. Next, after accumulating multiple times within one scanning period, the vertical scanning lines are transferred at high speed, the signal charges are shifted to the frame memory unit, and the frame memory unit conforms to a normal image format (for example, NTSC system). With this scanning method, an infrared image signal is taken out to an external circuit.

According to the present invention, the infrared signal charges are read out a plurality of times from the pyroelectric sensor within one scanning period, accumulated in the accumulation area in the vertical scanning line once, integrated a predetermined number of times, and then the signal charges are framed. High-speed transfer to memory,
By performing scanning as a normal imaging system, the accumulation time of one pyroelectric sensor can be shortened, the spatial resolution of the infrared image caused by heat leak due to heat conduction between pixels, and the Prevent deterioration.

Embodiment An embodiment of the present invention is shown in FIG. 1, FIG. 2, and FIG.
FIG. 1 schematically shows the entire configuration of an image pickup system according to an embodiment of the present invention, in which 30 is an image pickup unit, 31 is a frame memory unit, 32 is a horizontal CCD for horizontal scanning, and 33 is an output circuit. Basically, it has a frame transfer type CCD. ΦV is a drive pulse for vertical scanning of the imaging unit 30, φM is a drive pulse for vertical scan of the frame memory unit 31, and φM is a drive pulse for horizontal scanning of the horizontal CCD 32. FIG. 2 schematically shows a plan configuration of a unit pixel in the image pickup section 30 of FIG. 1, and FIG. 3 is a sectional view taken along the line II 'of FIG. To facilitate the description, the same components will be described with common numbers.

Here, 1 is a P-type semiconductor substrate, 2 is a field oxide film, 3 is a channel stop, and 4 is a diode for accumulating signal charges of the pyrosensor 16 and formed of an n ⁺ diffusion layer. 5 is a diode for injecting a bias charge into the storage diode 4, 6 is a gate for controlling the injection of bias electrification from the injection diode 4, and 7 is a control gate for reading the signal charge of the storage diode 4 into a vertical CCD storage region 9. , 8 are transfer gates on the vertical CCD 9, and 10 is a gate insulating film. Reference numeral 15 denotes a bump metal formed of Au or the like that electrically connects the storage diode 4 and the pyrosensor 16, 11 denotes an Al electrode that electrically connects the bump metal 15 and the storage diode 4, and 12 denotes an Al electrode.
An arbitrary voltage is externally applied to the injection diode 5 by an electrode. 13 is an interlayer insulating film, 14 is also an interlayer insulating film, 16 is a pyrosensor film made of PLT or the like as described above, 17 is adhered to a lower portion of the pyrosensor film 16 (opposite to the incident light side), and Separated and independent current collecting electrodes (electrodes that collect signal charges of the pyrosensor film for each pixel) and are formed of NiCr or the like. Reference numeral 20 denotes a common electrode for all pixels bonded to the upper portion (on the incident light side) of the pyrosensor film 16 and is made of NiCr or the like. hV is incident infrared light.

A is a transfer path connecting the storage diode 4 and the vertical CCD 9 and is connected to a transfer unit A21. B is another similar transfer path and is connected to a transfer unit B22. In the transfer path B, similarly to the transfer path A, a control gate 27 connects the storage diode 4 and the vertical CCD 9. As described above, the storage diode 4 is connected to the transfer paths A and B.
Are respectively connected to the vertical CCD 9. Next, the driving method of the present invention and the operation when the driving method is used will be described with reference to FIGS. 4 and 5. FIG. FIG. 4 shows a driving pulse according to the present invention, and the entire scanning system is repeated at regular intervals (33.3 msec). FIG. 5 schematically shows an electric equivalent circuit of the pixel portion and a potential during operation.

Now, the light chopper repeatedly opens and closes a plurality of times during one scanning period, and the pyrosensor output generates a positive charge and a negative charge based on this. Then, in synchronization with the opening and closing of the optical chopper, the control gate φi6 is turned on and the injection diode
A bias charge is injected from VOFD5 into the storage diode (FIG. 5 (b)). Next, the control gate φT
₁ 7, in synchronization with the opening and closing of the chopper light analogously .phi.T ₂ 27 ON
Then, the positive and negative charges of the stored signal charge for one optical chopper of the storage diode are separated from each other via transfer paths A and B,
Pyro signal charges are accumulated in the accumulation areas of the transfer units A and B in the vertical CCD 9 (FIG. 5 (c)). Next, after one scanning period, the vertical CCD is transferred at a high speed, and the integrated signal charge in the vertical CCD is transferred from the imaging unit 30 to the frame memory unit 32 at a high speed (FIG. 5 (d)). Then, the integrated signal charges are sequentially vertically transferred from the frame memory unit 32 in accordance with the standard of the normal imaging method, and are taken out to the outside via the horizontal CCD 32 and the output circuit 33 as an imaging signal output. In FIG. 5A, VT is a bias terminal of the common electrode 18 of the pyrosensor film.

Effect of the Invention As described above, in the present invention, the infrared signal charge is taken out of the pyroelectric sensor a plurality of times in response to the opening and closing of the light chopper several times within one scanning period,
Once the data is accumulated in the accumulation area in the vertical CCD. After accumulating a predetermined number of times according to the number of times the optical chopper is opened and closed,
The CCD is transferred at a high speed to transfer the integrated signal charge from the image pickup unit to the frame memory unit, and is taken out of the frame memory unit as an image pickup signal by scanning with a normal frame transfer CCD. Thus, the following effects can be obtained.

(1) Since the accumulation time for one pyroelectric sensor can be significantly shorter than the accumulation time determined in one scanning period (by a plurality of integration operations in one scanning period), the gap between pixels can be reduced. The deterioration of the spatial resolution of the infrared image due to the heat conduction can be greatly improved. For this reason, if the spatial resolution is the same, it is possible to greatly increase the density of pixels.

(2) If the pixel size is the same, the SIN can be significantly improved, and the infrared image can be improved. Here, the description has been made using the CCD as the scanning circuit, but the same effect can be obtained by using another solid-state scanning circuit such as a MOS.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of the overall configuration of an imaging system according to one embodiment of the present invention, FIG. 2 is a schematic plan configuration diagram of a unit pixel of the imaging unit in FIG. 1, and FIG. 3 is I in FIG. FIG. 4 is a schematic drive pulse waveform diagram of one embodiment of the present invention, and FIG.
The figure is a schematic driving potential diagram of one embodiment of the present invention,
FIG. 6 is a conceptual diagram of an equivalent circuit of a unit pixel and a driving potential showing a conventional example. 1 ... substrate, 4 ... n ⁺ diffusion layer (storage diode), 5 ...
... n ⁺ diffusion layer (injection diode), 6 ... control gate, 7 ... control gate, 27 ... control gate, 8 ... transfer electrode, 9 ... CCD transfer general, 11 ... Al
Electrode, 12: Al electrode, 15: Au bump, 16: Pyrosensor film, 17: Pyroelectric electrode, 18: Common electrode.

Claims (2)

(57) [Claims] 1. A semiconductor device, comprising: a frame memory unit; and an imaging unit. In the imaging unit, a first diode region of a conductivity type opposite to the semiconductor substrate is provided on a semiconductor substrate, and the first diode region is stored in the first diode region. A scanning line for scanning the signal charge, and on an electrode connected to the first diode region,
A pyroelectric infrared sensor is formed, wherein the infrared sensor generates positive and negative signal charges in response to opening and closing of an optical chopper. In the pyroelectric infrared imaging device, a second charge is injected into the first diode. , And a second control gate for reading out signal charges from the first diode to the scan line.
A pyroelectric infrared imaging apparatus comprising: one control gate; and an external bias or pulse applied to the second diode and each of the control gates. 2. A semiconductor device, comprising: a frame memory unit; and an image pickup unit, wherein the image pickup unit stores, on a semiconductor substrate, a first diode region of a conductivity type opposite to the semiconductor substrate and the first diode region. A pyroelectric infrared sensor is formed on an electrode connected to the first diode region, the scan line scanning a signal charge, and the infrared sensor detects positive and negative signals according to opening and closing of an optical chopper. In a pyroelectric infrared imaging device that generates electric charges, a second diode for injecting a bias electric charge into the first diode and a first control gate are provided, and a signal electric charge from the first diode is supplied to the scan line. Second and third control gates for reading are provided, and an arbitrary bias or pulse is externally connected to the second diode and each of the control gates. In the pyroelectric infrared imaging device for applying the voltage, the signal charge stored in the first diode is read out to a scan line at regular intervals, and the driving for scanning to an external circuit is performed a plurality of times within the constant period. The optical chopper is opened and closed, and in synchronization with the opening and closing of the optical chopper, a bias charge is injected into the first diode from the second diode via the first control gate, and the light In synchronization with opening and closing of the chopper,
The signal charge of the first diode is alternately transferred under an arbitrary gate on the scanning line via the second and third control gates, and the optical chopper is opened and closed a predetermined number of times within the fixed period. A method for driving a pyroelectric infrared imaging device, wherein the integrated signal charge on the scan line is scanned to an external circuit after performing the above operation.