JP3322078B2 - Solid-state imaging device and driving method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state imaging device such as a CCD image sensor, and more particularly to a solid-state imaging device having a built-in nonvolatile memory and a driving method thereof.

[0002]

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

On the other hand, a semiconductor image storage device having a built-in nonvolatile memory for each pixel of a solid-state imaging device is disclosed in, for example, JP-A-61-48972 and JP-A-2-2607.
No. 6, for example. JP-A-61-4897
2 (hereinafter referred to as Conventional Example 1).
Is an MNOS (Metal Nitride Oxide S / M) using a gate insulating film made of an oxide film and a nitride film having a charge trapping level in each pixel portion of an XY matrix solid-state imaging device.
An MNOS type nonvolatile analog memory is provided, and the source of the MNOS type nonvolatile analog memory is grounded via a photoelectric conversion element.

On the other hand, a semiconductor device disclosed in Japanese Patent Application Laid-Open No. 2-26076 (hereinafter referred to as Conventional Example 2) combines a volatile semiconductor memory device, a nonvolatile semiconductor memory device, and a photodiode to irradiate the photodiode. The converted optical signal is converted into an electric signal, and the data is transferred and stored in a nonvolatile semiconductor memory device.

[0005]

However, both of the prior arts 1 and 2 having the above-described configuration are of a non-destructive read-out type, in which information of each pixel is read out without being destroyed. Since the stored information is read out by passing a current through the storage device, the power consumption is large. In particular, in the case of the second conventional example, there is a problem that the power consumption is extremely large because a steady current flows.

SUMMARY OF THE INVENTION 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 imaging device capable of storing and reading information of each pixel and reading the information with low power consumption and a driving method thereof. It is to provide a method.

[0007]

A solid-state imaging device according to claim 1 is a solid-state imaging device of an interline transfer system, wherein the solid-state imaging device has a two-layer gate structure having a floating gate as a lower layer and includes a plurality of light receiving units. , And a vertical charge transfer section, and accumulates the signal charge of each light receiving section by sucking it into a floating gate as a Fowler-Nordheim (hereinafter referred to as Fowler-Nordheim) tunnel current, A non-volatile memory for reading out the signal charges to the vertical charge transfer unit by the FN tunnel operation is provided.

According to a second aspect of the present invention, there is provided a method for driving a solid-state image pickup device, comprising a two-layer gate structure having a floating gate as a lower layer, provided between each of a plurality of light receiving sections and a vertical charge transfer section. In an interline transfer type solid-state imaging device having a memory, signal charges photoelectrically converted by each light receiving unit are stored by being taken up as a FN tunnel current into a floating gate, and the signal charges stored in the floating gate are stored in a floating gate. -Read out to the vertical charge transfer section by the N tunnel operation.

According to a third aspect of the present invention, the solid-state imaging device is a solid-state imaging device of a frame transfer system, which has a two-layer gate structure having a floating gate as a lower layer and is provided corresponding to each of the plurality of light receiving sections. And the signal charge of each light receiving section is
A non-volatile memory is provided which stores the signal charge by absorbing it as an N tunnel current to a floating gate and reads out the signal charge to a light receiving unit by an FN tunnel operation.

According to a fourth aspect of the present invention, there is provided a method for driving a solid-state image pickup device, comprising: a non-volatile memory having a two-layer gate structure having a floating gate as a lower layer and provided for each of a plurality of light receiving units; In the solid-state imaging device of the frame transfer method, the signal charges photoelectrically converted in each light receiving unit are stored by being absorbed into a floating gate as an FN tunnel current, and the signal charges accumulated in the floating gate are stored in the FN. The data is read out to the light receiving unit by the tunnel operation.

[0011]

In an interline transfer type solid-state imaging device and a method of driving the same, a gate voltage is applied to a control gate corresponding to an upper layer gate of a two-layer gate structure, whereby barrier energy due to a gate insulating film on the lower surface side of the floating gate is reduced. Is the electron tunneling phenomenon, that is, FN
Pass through by tunneling. Thereby, electrons are injected from the light receiving portion into the floating gate. As a result, pixel information based on the signal charge photoelectrically converted by each light receiving unit is written to the floating gate and stored and held here. 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 out 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 the method of driving the same, a gate voltage is applied to a control gate corresponding to an upper layer gate of a two-layer gate structure to reduce barrier energy by a gate insulating film on the lower surface side of the floating gate. The electrons pass through by FN tunneling. Thereby, electrons are injected from the light receiving portion into the floating gate. As a result, pixel information based on the signal charge photoelectrically converted by each light receiving unit is written to the floating gate and stored and held here. On the other hand, by applying a read voltage to the transparent transfer electrode of each light receiving unit, the pixel information stored and held in the floating gate is read out to the light receiving unit again by the FN tunnel operation. That is, the pixel information is read by destructive reading.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows an interline transfer (I
1 is a configuration diagram illustrating an embodiment of the present invention applied to a T) type solid-state imaging device. In FIG. 1, a plurality of light receiving sections 11 including photodiodes and the like are two-dimensionally arranged in the horizontal and vertical directions, and convert incident light into signal charges having a charge amount corresponding to the light amount in pixel units. These light receiving units 11
Charge-coupled device (CCD; Charge C
and a plurality of vertical charge transfer units 12 for vertically transferring signal charges. These vertical charge transfer units 12 are, for example, four-phase transfer clocks Vφ1 to Vφ1.
The transfer is driven by Vφ4.

A non-volatile 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 sections 11 and the vertical charge transfer section 12. . A horizontal charge transfer unit 16 for horizontally transferring signal charges transferred from the vertical charge transfer unit 12 is provided below the vertical charge transfer unit 12 in the drawing.
Is provided. The horizontal charge transfer unit 16 is driven by, for example, two-phase transfer clocks Hφ1 and Hφ2. At the end of the transfer destination of the horizontal charge transfer section 16, a charge detection section 17 having, for example, a floating diffusion (FD) configuration for detecting a signal charge and converting the signal charge into a signal voltage is provided.

FIG. 2 shows a sectional structure around a light receiving section of a unit pixel. In FIG. 2, a p-well 22 is formed in an upper layer of an n-type semiconductor substrate 21, and the light receiving portion 11 is formed of an n-type diffusion layer 23 formed on the surface side of the p-well 22.
It has a junction photodiode configuration. Around the n-type diffusion layer 23 except for the vertical charge transfer section 12 side, ap ⁺ -type diffusion layer 24 serving as a channel stop section is formed.
On the other hand, the vertical charge transfer section 12 includes an n ⁻ -type diffusion layer 25 formed on the surface side of the p-well 22 and an insulating film 26 thereon.
, And 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 substrate surface between the light receiving section 11 and the vertical charge transfer section 12, and a floating gate electrode 13 is 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 thereon. As described above, the nonvolatile memory 15 has a two-layer gate structure having the floating gate electrode 13 as a lower layer and the control gate electrode 14 as an upper layer.

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

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

On the other hand, information stored in the floating gate electrode 13 is transferred to the transfer electrode 1 of the vertical charge transfer section 12.
4 by applying a positive read voltage Vro to FIG.
As shown in the potential diagram of FIG. That is,
Information stored in the nonvolatile memory 15 is read out to the vertical charge transfer unit 12 by destructive reading. The signal charge read out to the vertical charge transfer unit 12 is vertically transferred by the vertical charge transfer unit 12, further horizontally transferred by the horizontal charge transfer unit 16, converted to a signal voltage by the charge detection unit 17, and output. You.

As described above, the nonvolatile memory 15 is provided between each light receiving section 11 and the vertical charge transfer section 12 in the CCD solid-state imaging device of the interline transfer system, and has 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 time. The image information at this time is equivalent to one photograph. Therefore, the CCD solid-state imaging device having the memory function is useful for a still (still image) camera. In particular, since the stored information in the non-volatile memory 15 is read out to the vertical charge transfer unit 12 composed of the charge-coupled device by destructive readout, no DC current flows at the time of the readout. It is highly convenient when used for portable products.

FIG. 5 shows a modification of the structure of the nonvolatile memory 15. In this modification, as shown in FIG. 5, the first gate insulating film 28 of the nonvolatile memory 15 is formed thick, the floating gate electrode 13 is formed thereon, and the control is performed via the second gate insulating film 29. A structure in which the gate electrode 14 is formed is employed. According to this structure, assuming that the area of nonvolatile memory 15 in plan view is the same as that of the structure of FIG.
3 and the central portion of the control gate electrode 14 are raised, so that the substantial electrode area can be increased, and the capacitance also increases accordingly. In other words,
Non-volatile memory 15 of the same capacity with less exclusive area
Can be formed.

FIG. 6 shows a frame transfer (FT) type CC.
FIG. 13 is a configuration diagram showing another embodiment of the present invention applied to a D solid-state imaging device. The CCD solid-state imaging device of the frame transfer system includes a photosensitive unit 61 that performs photoelectric conversion on a pixel basis, a storage unit 62 that stores one field of signal charges photoelectrically converted by the photosensitive unit 61, and a storage unit 62. Line transfer unit 63 for transferring signal charges transferred one line at a time from
And a charge detection unit 64 provided at the transfer destination end of the line transfer unit 63 for converting signal charges into signal voltages. The storage unit 62 has a structure in which light is shielded so that external light is not mixed.

The photosensitive section 61 includes a plurality of light receiving sections 65.
They are provided in a dimensional array. Each of the light receiving units 65 in the vertical column is provided continuously with each other, and a transparent transfer electrode (not shown) is disposed on the upper part thereof, so that the signal charges photoelectrically converted by each of the light receiving units 65 are accumulated. It also has a function of a transfer unit for transferring to the unit 62. In addition, each light receiving section 65
A non-volatile memory 68 having a two-layer gate structure having a floating gate 66 in a lower layer and a control gate 67 in an upper layer is provided beside.

Next, the CC of the frame transfer system having the above configuration is described.
An imaging operation in the D solid-state imaging device will be described. First, when light is exposed during a certain exposure period, each light receiving unit 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, the signal charge of each light receiving section 65 is drawn by the floating gate 66 as an FN tunnel current and written by the same operation principle as in the previous embodiment, It is stored here.

On the other hand, when reading out the information stored and held in the floating gate 66, first, a process of sweeping out the signal charges accumulated so far in each light receiving unit 65 through the accumulation unit 62 and the line transfer unit 63. I do. In this manner, after each light receiving portion 65 is in a state where there is no unnecessary electric charge, a positive read voltage is applied to a transparent transfer electrode (not shown) of each light receiving portion 65, so that the data is stored 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, and further transferred one line at a time via the line transfer unit 63. The signal charges are converted into signal voltages by the charge detection unit 64 and output. Is done.

In each of the above embodiments, a case has been described in which the present invention is applied to an interline transfer CCD solid-state imaging device and a frame transfer CCD solid-state imaging device.
The same can be applied to a D solid-state imaging device.

[0027]

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

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view illustrating a cross-sectional structure around a light receiving unit of a unit pixel.

FIG. 3 is a potential diagram at the time of writing by FN tunneling.

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

FIG. 5 is a sectional view showing a modification of the structure of the nonvolatile memory.

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

[Explanation of symbols]

 11, 65 light receiving section 12 vertical charge transfer section 13, 66 floating gate 14, 67 control gate 15, 68 non-volatile memory 61 photosensitive section 62 storage section

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 27/148 H01L 21/8247 H01L 29/788 H01L 29/792

Claims (4)

(57) [Claims] 1. 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 charge-coupled device arranged for each vertical column of the plurality of light receiving portions. An interline transfer type solid-state imaging device having a plurality of vertical charge transfer portions comprising: a two-layer gate structure having a floating gate in a lower layer, wherein each of the plurality of light receiving portions and the vertical charge A signal charge of each light receiving unit is provided as a Fowler-Nordheim tunnel current and is accumulated by sucking the signal charge into the floating gate, and the signal charge is transferred to the vertical charge transfer unit by a Fowler-Nordheim tunnel operation. A solid-state imaging device comprising a nonvolatile memory for reading. 2. A plurality of two-dimensionally arranged light receiving portions for converting incident light into signal charges having a charge amount corresponding to the light amount, and a charge-coupled device arranged for each vertical column of the plurality of light receiving portions. And a nonvolatile memory provided between each of the plurality of light receiving units and the vertical charge transfer unit, having a two-layer gate structure having a floating gate as a lower layer. In the solid-state imaging device of the interline transfer method, the signal charge photoelectrically converted by the light receiving unit is accumulated by sucking the signal charge as the Fowler-Nordheim tunnel current to the floating gate, and the signal charge accumulated in the floating gate is Fowler -A method for driving a solid-state imaging device, wherein reading is performed to the vertical charge transfer unit by a Nordheim tunnel operation. 3. A photosensitive section comprising a plurality of two-dimensionally arranged light receiving sections for converting incident light into signal charges having a charge amount corresponding to the amount of light, and temporarily converting the signal charges photoelectrically converted by said photosensitive section. A solid-state imaging device of a frame transfer system having a storage unit for storing data in a plurality of light receiving units, each of the plurality of light receiving units having a two-layer gate structure having a floating gate as a lower layer, A solid-state memory comprising: a non-volatile memory that accumulates a signal charge of a portion as a Fowler-Nordheim tunnel current by sucking the signal charge into the floating gate and reads out the signal charge to the light receiving portion 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, and In a solid-state imaging device of a frame transfer system having a photosensitive unit including a non-volatile memory provided corresponding to each of the light receiving units and a storage unit for temporarily storing signal charges photoelectrically converted by the photosensitive unit, The signal charge photoelectrically converted by the light receiving unit is accumulated by sucking it into the floating gate as a Fowler-Nordheim tunnel current, and the signal charge accumulated in the floating gate is read out to the light receiving unit by a Fowler-Nordheim tunnel operation. A method for driving a solid-state imaging device, comprising: