JPH08340100A - Solid-state image pickup device and its driving method - Google Patents

Abstract

PURPOSE: To provide a solid-state image pickup device which can store and hold information on each picture element with low power consumption and from which the information can be read out with low power consumption. CONSTITUTION: An interline transfer type CCD solid-state image pickup device provided with a plurality of two-dimensionally arranged light receiving sections 11 and a plurality of vertical charge transferring sections 12 composed of charge-coupled devices(CCD) arranged at every vertical row of the sections 11. Nonvolatile memories 15 each of which is constituted in a two-layer gate structure having a floating gate 13 as its lower layer and a control gage 14 as its upper layer are respectively provided between the light receiving sections 11 and the vertical charge transferring sections 12 and signals photoelectrically converted at the sections 11 are accumulated in the floating gates 13 by sucking up the signals to the gates 13 as F-N tunnel currents and the signal charges accumulated in the gates 13 are read out to the transferring section 12 through F-N tunnel operations.

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 such as a CCD image sensor, and more particularly to a solid-state image pickup device having a built-in nonvolatile memory and a driving method thereof.

[0002]

2. Description of the Related Art Since a solid-state image pickup device such as a CCD image sensor does not have a memory function, if pixel (picture element) information is not sequentially read by a dynamic operation, the information will be erased. Therefore, conventionally, the pixel information is once read out from the CCD image sensor, and the A / D
It had to be converted into digital image information by a converter and stored in an external memory for storage.

On the other hand, a semiconductor image storage device in which a non-volatile memory is built in each pixel of a solid-state image pickup device is disclosed in, for example, JP-A-61-48972 and JP-A-2-2607.
It is disclosed in Japanese Patent Publication No. 6 and the like. Japanese Patent Laid-Open No. 61-4897
The semiconductor image storage device disclosed in Japanese Unexamined Patent Publication No.
Is referred to as MNOS (Metal Nitride Oxide S) using a gate insulating film made of an oxide film and a nitride film having a charge trap level in each pixel portion of an XY matrix type solid-state imaging device.
An emiconductor) type nonvolatile analog memory is provided, and the source of this MNOS type nonvolatile analog memory is grounded via a photoelectric conversion element.

On the other hand, the semiconductor device disclosed in Japanese Patent Application Laid-Open No. 2-26076 (hereinafter referred to as reference example 2) is a combination of a volatile semiconductor memory device, a non-volatile semiconductor memory device and a photodiode, and the photodiode is irradiated. The optical signal thus converted is converted into an electric signal, and the data is transferred to and stored in the nonvolatile semiconductor memory device.

[0005]

However, in both the conventional example 1 and the conventional example 2 having the above-described structure, the nondestructive read is performed without destroying the information of each pixel, and the nonvolatile analog memory (nonvolatile semiconductor) is used. Since a current is passed through the memory device) to read the stored information, there is a problem that the power consumption is large, and particularly in the case of the conventional example 2, a steady current flows and therefore the power consumption is extremely large.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a solid-state image pickup device capable of storing and holding information of each pixel and reading the same with low power consumption and its driving. To provide a method.

[0007]

A solid-state image pickup device according to claim 1 is an interline transfer type solid-state image pickup device having a two-layer gate structure having a floating gate in a lower layer. Is provided between each of the above and the vertical charge transfer section, and the signal charge of each light receiving section is accumulated by being absorbed into the floating gate as a Fowler-Nordheim (hereinafter, referred to as FN (Fowler-Nordheim)) tunnel current, It has a configuration including a non-volatile memory for reading the signal charges to the vertical charge transfer unit by an FN tunnel operation.

According to a second aspect of the present invention, there is provided a method of driving a solid-state image pickup device, which has a two-layer gate structure having a floating gate as a lower layer and is provided between each of a plurality of light receiving portions and a vertical charge transfer portion. In an interline transfer type solid-state imaging device having a memory, the signal charges photoelectrically converted in each light receiving unit are absorbed by being absorbed as an FN tunnel current in a floating gate, and the signal charges accumulated in the floating gate are accumulated in the F gate. Read-out is performed to the vertical charge transfer unit by the -N tunnel operation.

A solid-state image pickup device according to a third aspect of the present invention is a frame transfer type solid-state image pickup device having a two-layer gate structure having a floating gate as a lower layer and provided corresponding to each of a plurality of light receiving portions. And the signal charge of each light receiving part is
The nonvolatile memory has a configuration in which a non-volatile memory that stores the N charge as a N tunnel current by sucking it up in a floating gate and reads the signal charge to a light receiving portion by an FN tunnel operation is provided.

According to a fourth aspect of the present invention, there is provided a method of driving a solid-state image pickup device, which comprises a non-volatile memory having a two-layer gate structure having a floating gate as a lower layer and provided corresponding to each of a plurality of light receiving portions. In the frame transfer type solid-state image pickup device having the above-mentioned, the signal charges photoelectrically converted in each light receiving section are accumulated by being absorbed into the floating gate as an FN tunnel current, and the signal charges accumulated in the floating gate are accumulated in the FN. The data is read out to the light receiving portion by the tunnel operation.

[0011]

In the interline transfer type solid-state imaging device and its driving method, by applying a gate voltage to the control gate corresponding to the upper gate of the two-layer gate structure, the barrier energy by the gate insulating film on the lower surface side of the floating gate is applied. Electron is a tunnel phenomenon, that is, FN
Pass through by tunneling. As a result, electrons are injected from the light receiving portion to the floating gate. As a result, pixel information based on the signal charges photoelectrically converted by each light receiving unit is written in the floating gate and stored and held therein. On the other hand, by applying a read voltage to the transfer electrode of the vertical charge transfer unit, the pixel information stored and held in the floating gate is read to the vertical charge transfer unit by the FN tunnel operation. That is, the pixel information is read by destructive reading.

In the frame transfer type solid-state imaging device and its driving method, by applying a gate voltage to the control gate corresponding to the upper gate of the two-layer gate structure, the barrier energy due to the gate insulating film on the lower surface side of the floating gate is reduced. The electrons pass through by FN tunneling. As a result, electrons are injected from the light receiving portion to the floating gate. As a result, pixel information based on the signal charges photoelectrically converted by each light receiving unit is written in the floating gate and stored and held therein. On the other hand, by applying a read voltage to the transparent transfer electrode of each light receiving portion, the pixel information stored and held in the floating gate is read back to the light receiving portion by the FN tunnel operation. That is, the pixel information is read by destructive reading.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows an interline transfer (I
It is a block diagram which shows one Example of this invention applied to the T) system solid-state imaging device. In FIG. 1, a plurality of light receiving portions 11 including photodiodes and the like are two-dimensionally arrayed in the horizontal and vertical directions, and convert incident light into pixel-unit signal charges corresponding to the amount of light. These light receiving parts 11
Charge-coupled device (CCD; Charge C) for each vertical column of
a plurality of vertical charge transfer units 12 which are vertically coupled devices and which vertically transfer signal charges. These vertical charge transfer units 12 have, for example, four-phase transfer clocks Vφ1 to Vφ1.
The transfer is driven by Vφ4.

A nonvolatile memory 15 having a two-layer gate structure having a floating gate 13 in a lower layer and a control gate 14 in an upper layer is provided between each of the light receiving units 11 and the vertical charge transfer unit 12. . Below the vertical charge transfer unit 12 in the drawing, a horizontal charge transfer unit 16 that horizontally transfers the signal charges transferred from the vertical charge transfer unit 12 is provided.
Is provided. The horizontal charge transfer section 16 is transfer-driven by, for example, two-phase transfer clocks Hφ1 and Hφ2. At the end of the transfer destination of the horizontal charge transfer unit 16, a charge detection unit 17 having, for example, a floating diffusion (FD) configuration that detects the signal charge and converts it into a signal voltage is provided.

FIG. 2 shows a sectional structure around the light receiving portion of the unit pixel. In FIG. 2, a p-well 22 is formed in the upper layer of the n-type semiconductor substrate 21, and the light receiving part 11 is an np diffusion layer 23 formed on the surface side of the p-well 22.
It has a junction photodiode configuration. A p ⁺ -type diffusion layer 24 serving as a channel stop portion is formed around the n-type diffusion layer 23 except for the vertical charge transfer portion 12 side.
On the other hand, in the vertical charge transfer unit 12, the n ⁻ type diffusion layer 25 formed on the surface side of the p well 22 and the insulating film 26 above the n ⁻ type diffusion layer 25.
And the transfer electrodes 27 arranged at a constant pitch in the transfer direction (direction perpendicular to the paper surface).

A first gate insulating film 28 is formed on the surface of the substrate between the light receiving portion 11 and the vertical charge transfer portion 12, and a floating gate electrode 13 is further formed thereon. A second gate insulating film 29 is formed on the floating gate electrode 13, and a control gate electrode 14 is further formed on the second gate insulating film 29. In this way, the non-volatile memory 15 is formed by the two-layer gate structure having the floating gate electrode 13 in the lower layer and the control gate electrode 14 in the upper layer.

Next, the image pickup operation in the CCD solid-state image pickup device of the interline transfer type having the above construction will be described. First, when exposed in a certain exposure period, each light receiving section 11 performs photoelectric conversion of the incident light into a signal charge having a charge amount corresponding to the light amount. When the positive gate voltage Vcg is applied to the control gate electrode 14 of the nonvolatile memory 15 after the end of the exposure period, the electrons e pass through the barrier energy by the first gate insulating film 28 by the tunnel phenomenon, that is, FN tunneling. As a result, electrons e are injected from the n-type diffusion layer 23 of the light receiving unit 11 into the floating gate electrode 13 of the nonvolatile memory 15.

At this time, as shown in the potential diagram of FIG. 3, the FN tunnel current is absorbed by the floating gate electrode 13 by the amount of the signal charge photoelectrically converted by the light receiving portion 11. As a result, the pixel information based on the signal charges photoelectrically converted by each light receiving unit 11 is written in the floating gate electrode 13 of the non-volatile memory 15 and is stored and held here.

On the other hand, the information stored and held in the floating gate electrode 13 is transferred to the transfer electrode 1 of the vertical charge transfer section 12.
2 by applying a positive read voltage Vro to FIG.
As shown in the potential diagram of No. 3, the data is read to the vertical charge transfer unit 12 by the FN tunnel operation. That is,
The information stored in the non-volatile memory 15 is read by the vertical charge transfer unit 12 by destructive reading. The signal charges read to the vertical charge transfer unit 12 are vertically transferred by the vertical charge transfer unit 12, further horizontally transferred by the horizontal charge transfer unit 16, and then converted into a signal voltage by the charge detection unit 17 and output. It

As described above, the interline transfer type CCD solid-state image pickup device is provided with the nonvolatile memory 15 between each light receiving portion 11 and the vertical charge transfer portion 12 so as to have a memory function. Since the pixel information of each light receiving unit 11 can be stored and held in the non-volatile memory 15, the image information can be arbitrarily extracted in terms of time. The image information at this time corresponds to one photograph. Therefore, the CCD solid-state imaging device having this memory function is useful for a still (still image) camera. In particular, since the stored information in the nonvolatile memory 15 is read out to the vertical charge transfer unit 12 formed of a charge-coupled device by destructive reading, a direct current does not flow during the reading, so that the power consumption can be reduced. As a result, it is highly convenient to use for portable products.

FIG. 5 shows a modification of the structure of the nonvolatile memory 15. In this modified example, as shown in FIG. 5, the first gate insulating film 28 of the non-volatile memory 15 is formed thick, the floating gate electrode 13 is formed on the first gate insulating film 28, and control is performed via the second gate insulating film 29. The structure in which the gate electrode 14 is formed is adopted. According to this structure, assuming that the area of the nonvolatile memory 15 in plan view is the same as that of the structure of FIG. 2, the floating gate electrode 1
3 and the central portion of the control gate electrode 14 are raised, the substantial electrode area can be increased, and the capacitance is increased accordingly. In other words,
Non-volatile memory 15 of the same capacity with a smaller occupied area
Can be formed.

FIG. 6 shows a frame transfer (FT) type CC.
It is a block diagram which shows the other Example of this invention applied to the D solid-state imaging device. This frame transfer type CCD solid-state imaging device includes a photosensitive section 61 that performs photoelectric conversion in pixel units, an accumulating section 62 that accumulates the signal charges for one field photoelectrically converted by the photosensitive section 61, and the accumulating section 62. From the line transfer unit 63 for transferring the signal charges transferred from the
And a charge detection unit 64 provided at the end of the transfer destination of the line transfer unit 63 to convert the signal charge into a signal voltage. The storage unit 62 has a structure that is shielded so that external light is not mixed.

The photosensitive section 61 has a plurality of light receiving sections 65.
They are arranged in a dimension. Further, the light receiving units 65 in the vertical column are provided in series with each other, and a transparent transfer electrode (not shown) is arranged on the upper part thereof to accumulate the signal charges photoelectrically converted by the respective light receiving units 65. It also has a function of a transfer unit for transferring to the unit 62. In addition, each light receiving unit 65
A non-volatile memory 68 having a two-layer gate structure, which has a floating gate 66 in a lower layer and a control gate 67 in an upper layer, is provided next to the.

Next, the CC of the frame transfer system having the above configuration
An image pickup operation in the D solid-state image pickup device will be described. First, when exposed in a certain exposure period, each light receiving section 65 performs photoelectric conversion of incident light into a signal charge having a charge amount corresponding to the light amount. After the end of the exposure period, the nonvolatile memory 68
When a positive gate voltage is applied to the control gate 67 of, the signal charge of each light receiving portion 65 is written by being absorbed in the floating gate 66 as an FN tunnel current according to the same operation principle as in the previous embodiment. It is stored and held here.

On the other hand, when reading the information stored and held in the floating gate 66, first, a process of sweeping away the signal charges accumulated in each light receiving section 65 up to that point via the accumulation section 62 and the line transfer section 63. I do. In this way, after each light receiving portion 65 is made to have no unnecessary electric charge, a positive read voltage is applied to the transparent transfer electrode (not shown) of each light receiving portion 65 to store it in the floating gate 66. The held information is read out to each light receiving unit 65 by the FN tunnel operation. Then, the signal charges read out to the respective light receiving units 65 are transferred to the storage unit 62, further transferred line by line via the line transfer unit 63, and then converted into a signal voltage by the charge detection unit 64 and output. To be done.

In each of the above embodiments, the case where the invention is applied to the CCD solid-state image pickup device of the interline transfer system and the CCD solid-state image pickup device of the frame transfer system has been described. However, the CC of the frame interline transfer (FIT) system is used.
The same can be applied to the D solid-state imaging device.

[0027]

As described above, according to the present invention,
A non-volatile memory is provided for each light-receiving part, and each pixel information is stored in this non-volatile memory, and the information is read by destructive reading, so that a direct current flows when reading. Therefore, storage and reading of information of each pixel can be realized with low power consumption.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention applied to an interline transfer type CCD solid-state imaging device.

FIG. 2 is a sectional view showing a sectional structure around a light receiving portion of a unit pixel.

FIG. 3 is a potential diagram during writing by FN tunneling.

FIG. 4 is a potential diagram at the time of reading by FN tunneling.

FIG. 5 is a cross-sectional view showing a modified example of the structure of the nonvolatile memory.

FIG. 6 is a configuration diagram showing an embodiment of the present invention applied to a frame transfer type CCD solid-state imaging device.

[Explanation of symbols]

 11, 65 Light receiving part 12 Vertical charge transfer part 13, 66 Floating gate 14, 67 Control gate 15, 68 Non-volatile memory 61 Photosensitive part 62 Storage part

Claims (4)

[Claims] 1. A plurality of light receiving parts arranged two-dimensionally for converting incident light into a signal charge having a charge amount corresponding to the light amount, and a charge-coupled device arranged in each vertical column of the plurality of light receiving parts. An interline transfer type solid-state imaging device having a plurality of vertical charge transfer parts each comprising a plurality of vertical charge transfer parts, wherein each of the plurality of light receiving parts and the vertical charge has a two-layer gate structure having a floating gate in a lower layer It is provided between the transfer section and the signal charge of each light receiving section is accumulated as it is absorbed by the floating gate as a Fowler-Nordheim tunnel current, and the signal charge is stored in the vertical charge transfer section by the Fowler-Nordheim tunnel operation. A solid-state imaging device comprising a nonvolatile memory for reading. 2. A plurality of light receiving sections arranged two-dimensionally for converting incident light into a signal charge having a charge amount corresponding to the light quantity, and a charge coupled device arranged in each vertical column of the plurality of light receiving sections. And a non-volatile memory having a two-layer gate structure having a floating gate as a lower layer and provided between each of the plurality of light receiving units and the vertical charge transfer unit. In an interline transfer type solid-state imaging device having, the signal charges photoelectrically converted by the light receiving unit are accumulated as a Fowler-Nordheim tunnel current by being absorbed in the floating gate, and the signal charges accumulated in the floating gate are accumulated by the Fowler. -A method for driving a solid-state imaging device, characterized in that the vertical charge transfer section is read by a Nordheim tunnel operation. 3. A photosensitive unit including a plurality of light receiving units arranged two-dimensionally for converting incident light into a signal charge having a charge amount corresponding to the amount of light, and the signal charge photoelectrically converted by the photosensitive unit is temporarily A solid-state image pickup device of a frame transfer system having a storage unit for storing light in each of the plurality of light receiving units, the two-layer gate structure having a floating gate in a lower layer, the light receiving unit being provided for each of the plurality of light receiving units. Solid state characterized by including a non-volatile memory for accumulating the signal charge of a part in the form of a Fowler-Nordheim tunnel current by absorbing it to the floating gate and reading the signal charge to the light receiving part by a Fowler-Nordheim tunnel operation. Imaging device. 4. A two-layer gate structure having a plurality of two-dimensionally arranged light receiving portions for converting incident light into signal charges having a charge amount corresponding to the amount of light and a floating gate as a lower layer, In a solid-state imaging device of a frame transfer system having a photosensitive portion formed of a non-volatile memory provided corresponding to each of the light receiving portions, and an accumulating portion for temporarily accumulating signal charges photoelectrically converted by the photosensitive portion, The signal charges photoelectrically converted in the light receiving unit are accumulated as a Fowler-Nordheim tunnel current by being absorbed in the floating gate, and the signal charges accumulated in the floating gate are read out to the light receiving unit by Fowler-Nordheim tunnel operation. A method for driving a solid-state imaging device, comprising: