JP2000023028A - Digital still camera - Google Patents

Abstract

(57) [Problem] To provide a MOS type imaging element manufactured by using a thin film technique, which enables high-definition image capturing and obtains a practical image capturing speed. SOLUTION: An M manufactured by a thin film technology as an imaging device is provided.
An OS-type imaging device 30 is disposed in the imaging unit housing 22, and the exposure time of light from the subject to the MOS-type imaging device 30 is controlled by a mechanical shutter that opens and closes at high speed.
By taking out the charges accumulated in the MOS type image pickup device 30 in a line-sequential manner, the image can be picked up. With such a configuration, since a MOS type imaging element having a high aperture ratio is used, good characteristics can be maintained even when the definition is increased to, for example, 5 million pixels or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital still camera, and more particularly, to a high-definition digital still camera using a solid-state imaging device which can be manufactured by using a TFT (thin film transistor) manufacturing process.

[0002]

2. Description of the Related Art Conventional digital still cameras include:
The subject image is captured by a CCD (Charge Coupled Device) imaging device via an optical system, and the image signal from the CCD imaging device is subjected to image processing, compressed, and stored in a built-in or a flash memory or the like mounted on a card. It has become. As a display medium, a liquid crystal display device (LC
D), a television, and a personal computer can be used.

[0003]

However, in a CCD image pickup device used in a conventional digital still camera, a data transfer CCD and a pixel photodiode are formed in an image sensor area, so that a high definition of about 5 million pixels is required. If an attempt is made to obtain a suitable CCD image pickup device, the characteristics will be limited, and it is difficult to achieve higher definition.

On the other hand, a TFT (thin film) formed on an insulating substrate
The in-film transistor) has a problem that the operation speed is low because line-sequential scanning and image capturing are performed, and a practical shutter speed cannot be obtained.

The problem to be solved by the present invention is to provide a digital still using a MOS type image pickup device manufactured by using a thin film technology capable of capturing a high-definition image and obtaining a practical image capturing speed. The realization of a camera.

[0006]

According to the first aspect of the present invention,
A digital still camera, in which a plurality of photoelectric conversion units each composed of a MOS type photo sensor having upper and lower gate electrodes are arranged in a matrix, and a subject is formed on a light detection surface of the MOS type image sensor. And a shutter for exposing a light detection surface of the MOS type image sensor for a predetermined time.

Therefore, according to the first aspect of the present invention, the MOS
Since all the photoelectric conversion units including the image sensor can be exposed at the same time, the opening and closing of the shutter can be accelerated,
For this reason, image data with little blur can be obtained even for a fast-moving subject.

According to a second aspect of the present invention, there is provided the digital still camera according to the first aspect, wherein the photoelectric conversion unit includes a digital camera.
A gate electrode facing the semiconductor layer is provided on both sides of a semiconductor layer having Si and a source / drain provided in the semiconductor layer via a gate insulating film, and a sense electrode is provided on the one gate electrode. A gate bias and a reset bias are applied, and a read selection signal is supplied to the other gate electrode. In the photoelectric conversion unit according to the second aspect of the present invention, the on / off ratio of the drain current can be set to about six digits by short-time exposure to light in the visible light wavelength range, so that extremely high-definition image data is captured. be able to. In addition, since control is performed with a structure having a gate electrode above and below, each photoelectric conversion unit can be mounted at a high density, and high-definition image data can be captured.

According to a third aspect of the present invention, there is provided the digital still camera according to the first or second aspect, wherein all of the photoelectric conversion units constituting the MOS type image pickup device simultaneously take in light for a predetermined time by opening and closing the shutter. It is characterized by performing.

According to a fourth aspect of the present invention, there is provided the digital still camera according to any one of the first to third aspects,
The high-speed shutter is a mechanical shutter.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of a digital still camera according to the present invention will be described below based on a typical example shown in the drawings. FIG. 1 is a perspective view illustrating the appearance of the digital still camera according to the present embodiment. FIG. 2 is an explanatory cross-sectional view illustrating a cross-section of the imaging unit of the digital still camera according to the present embodiment. As shown in the figure, the digital still camera includes a camera body 1, an optical system such as a lens unit, and an imaging unit 2 having a MOS imaging device.

The camera body 1 has a display 1 on its back.
0, a mode setting key 12a. The mode setting key 12a is a key for switching between a photographing mode for photographing an image and recording the image in an image memory described later and a reproduction mode for reproducing the recorded image. The display unit 10
It is configured by a liquid crystal display device, and functions as a viewfinder for displaying an image captured by the imaging unit 2 (monitoring mode) in the shooting mode, and functions as a display for displaying a recorded image in the playback mode. The configuration of the display unit 10 will be described later.

The camera body 1 has a power key 1 on its upper surface.
1, a shutter key 12b, a "+" key 12c,
It has a “−” key 12 d and a serial input / output terminal 13. The power key 11 can be operated by sliding.
A key for turning on / off the power of the digital still camera.

The shutter key 12b is set to M
A key for instructing the opening and closing of a mechanical shutter for taking in an image to the OS-type imaging device. In addition,
About MOS type image sensor and mechanical shutter,
It will be described later.

"+" Key 12c and "-" key 12d
Is used to select image data to be displayed on the display unit 10 from the image data recorded in the image memory in the reproduction mode, and to set conditions for recording / reproduction.
The serial input / output terminal 13 is a terminal for connecting a cable for communicating with an external device (a personal computer, a printer, or the like).

Next, the configuration of the imaging section 2 will be described with reference to FIG. The imaging unit 2 includes a lens 2 that forms an image to be captured.
1 is provided in a lens barrel 23 formed in the imaging unit housing 22. In the imaging unit housing 22, a MOS type imaging device 3 is provided at a position where an image is formed by the lens 21.
0 is arranged. In addition, a mechanical shutter 24 is provided inside the lens 21 of the lens barrel 23 so as to perform light incidence (exposure) to the MOS image sensor 30 for a predetermined time by opening and closing. The imaging unit 2 is attached so as to be rotatable up and down 360 ° around an axis connected to the camera body 1.

The structure of the MOS type image pickup device 30 will be described with reference to FIGS. FIG. 3 is a cross-sectional view showing the photoelectric conversion element 31 constituting one pixel of the MOS type imaging element 30. FIG. 4 is a circuit diagram of the MOS image sensor 30.

The MOS type image pickup device 30 used in this embodiment
As shown in FIG. 3, the photoelectric conversion element 31 provided in
A lower gate electrode 33 is formed on the insulating substrate 32, and the insulating substrate 32 including the lower gate electrode 33 is formed.
A lower gate insulating film 34 is formed so as to cover.
On the lower gate insulating film 34, a semiconductor thin film 35 made of intrinsic amorphous silicon is formed at a position facing the lower gate electrode 33. On both sides of the semiconductor thin film 35, a source electrode 36 and a drain electrode 37 are provided as shown in FIG. These source electrodes 36
The drain electrode 37 is ohmically connected to the semiconductor thin film 35 via n ⁺ silicon layers 38 and 39. The semiconductor thin film 35, the lower gate insulating film 34, the lower gate electrode 33, the source electrode 36, the drain electrode 37, and the like constitute an inverted staggered lower MOS transistor.

The insulating substrate 32 on which the source electrode 36, the drain electrode 37, the semiconductor thin film 35 and the like are formed as described above is covered with a transparent upper gate insulating film 40. On the upper gate insulating film 40, an upper gate electrode 41 that is transparent to visible light is formed at a position facing the lower gate electrode 33. Thus, the upper gate electrode 41, the upper gate insulating film 40, the semiconductor thin film 3
5, a source electrode 36, a drain electrode 37 and the like constitute a coplanar type upper MOS transistor. In the photoelectric conversion element 31 having such a configuration, light from the subject side is incident on the upper gate electrode 41, and this incident light is transmitted through the upper gate electrode 41 and the upper gate insulating film 40 and is incident on the semiconductor thin film 35. It has become. That is, the photoelectric conversion element 31 is arranged such that the upper gate electrode 41 faces the lens 21. As described above, the photoelectric conversion element 31 of the MOS imaging device 30 according to the present embodiment is a so-called double gate MOS photosensor.

Then, the MOS type image pickup device 3 of this embodiment
0 indicates that a large number of photoelectric conversion elements 31 are arranged in a matrix as shown in FIG. As shown in the figure, each photoelectric conversion element 31 has a lower gate electrode 33 connected to a lower gate driver 42 via a lower gate drive line 43, and a drain electrode 37 connected to a signal line 44. .

The MOS type image pickup device 30 is composed of two areas, a sensor array block 45 and a data select block 46. The above-described photoelectric conversion element 31 is disposed in the sensor array block 45.
In the data select block 46, one end of the switching element Q is connected to the signal line 44. The other end of the switching element Q is connected to the drain driver 48. The switching element Q is a TFT
It is a MOS transistor created by process technology,
The gate is connected to the data selector 49, and a voltage selectively output from the data selector 49 is applied to the gate of the switching element Q, whereby a predetermined voltage is supplied from the drain driver 48 to the signal line 44. You. The upper gate electrode 41 of the photoelectric conversion element 31 is
The upper gate drive line 51 is connected to an upper gate driver 52. Further, the source electrode 36 of the photoelectric conversion element 31 is grounded as shown in FIGS. The drain driver 48 supplies a voltage of a predetermined value to the signal line 44 according to an ON signal from the data selector 49. Thereafter, in a state where the switching element Q is opened by the OFF signal of the data selector 49, the selected one row of the photoelectric conversion elements 31 flows a drain current corresponding to the amount of incident light. Then, the voltage of the signal line 44 attenuated by the drain current is again changed by the ON signal from the data selector 49 to the drain driver 4.
8 and amplified by an internal buffer circuit and output terminal V
Output to out.

The MOS type imaging device 30 used in this embodiment
In this example, an offset bias is applied to the upper gate electrode 41 in synchronization with a read selection signal supplied to the lower gate electrode 33. By applying the offset bias in this manner, the lower gate electrode 33
Is formed, and a drain current flows according to the charge accumulated in the channel in accordance with the amount of incident light from the subject, thereby enabling photoelectric conversion. This MOS type imaging device 30
Then, by sequentially selecting with the data selector 49,
Data from all the pixels can be sequentially extracted from the drain driver 48 as the output voltage Vout for each address line. In order to reset all the pixels, if a reset voltage is applied to all the lines of the upper gate electrode 41 which is a sense gate, the accumulated charges are released to be in a reset state.

In this embodiment, data can be taken in between the time when the mechanical shutter 24 is opened and the time when the mechanical shutter 24 is closed. The reading of the output voltage Vout is performed at a low speed because the TFT formed by the TFT process technique is used as described above.
Carriers accumulated in 0 are predominantly due to optical excitation, and carriers due to thermal excitation can be sufficiently ignored for about 20 seconds at room temperature, so that data does not change even at low speed reading. For this reason, an imaging device having a sufficient function can be realized even when manufactured by the TFT process technology.

FIG. 5 is a block diagram showing a circuit configuration of the digital still camera of FIG. As shown in the figure, the circuit of the digital still camera includes a display unit 10, key input units 12a, 12b, 12c, and 12d, and a plurality of photoelectric conversion units (imaging pixels) 31 arranged in a matrix. MOS-type image pickup device 30 that accumulates electric charges in accordance with the intensity of sample, sample-and-hold circuit 53, and A / D converter 5
4, a drive driver 55, and a timing generator 5
6, a color process circuit 57, and a DMA (Direct Mem
ory Access) controller 58, DRAM 59, recording memory 60, key input units 12a, 12b, 12
c, a CPU (Central Processing Unit) 61 that executes the stored program in accordance with the commands from the 12d and controls each circuit unit of the digital still camera, an image compression / decompression circuit 62, a VRAM controller 63, and a VR.
An AM 64 and a digital video encoder 65 are provided.

The operation of the above circuit in the photographing mode will be described. There are two operation modes in the photographing mode, which are divided into a monitoring mode for displaying a photographed image on the display unit 10 and an image recording mode for recording a photographed image as image data.

In the monitoring mode, the CPU 61 operates the timing generator 56 every predetermined imaging cycle.
In addition, the MOS type image pickup device 30 is driven by controlling the color process circuit 57, and the MOS type image pickup device 30 converts the electric signal Se converted according to the light amount of the image captured based on the drive signal Sp output from the drive driver 55. Are sequentially output to the sample fold circuit 53. The sample fold circuit 53 generates an effective part S of the electric signal Se.
e ′ is output to the A / D converter 54. A / D converter 54
Converts the effective portion Se ′ into digital data Sd and outputs it to the color process circuit 57,
Outputs YUV data, which is luminance / color difference digital data, from the digital data Sd to the DMA controller 58. The DMA controller 58 converts the YUV data into a DRA
Record and update in M59.

The CPU 61 transfers one frame of YUV data transferred from the DMA controller 58 to the DRAM 5.
9 and read out from VRAM controller 63
Write to RAM64. Further, the digital video encoder 65 reads out one frame of YUV data from the VRAM 64 in a line-sequential manner via the VRAM controller 63 at regular intervals, and displays the analog video signal Sa on the display unit 10.
Output to

The serial input / output terminal 13 is an input / output terminal for the CPU 61 to perform serial transfer of data with an external device.

Key input sections 12a, 12b, 12c, 12
d is composed of a mode setting key 12a, a shutter key 12b, a "+" key 12c, and a "-" key 12d arranged on the camera body 1, and inputs a command to the CPU 61 in accordance with an input from each of these keys. I do.

Next, the image recording mode will be described.
First, the image recording mode is set by the mode setting key 12a, the subject is captured by the imaging unit 2, and the display unit 10 monitors the subject. Before photographing, a signal voltage of 0 (V) from the upper gate driver 52 is applied to the upper gate electrode 41 of all the photoelectric conversion elements 31, and at the same time, the lower gate driver 4 is applied to the lower gate electrode 33 of all the photoelectric conversion elements 31.
The signal voltage of 2 to 10 (V) is applied, and the signal line 44
Is supplied with a voltage of 10 (V). For this reason, the carriers accumulated in the semiconductor thin film 35 of all the photoelectric conversion elements 31 are released and enter a reset state. When the operator presses the shutter key 12b of the digital still camera,
The CPU 61 controls the timing generator 56 and the color process circuit 57 to stop the transfer operation. At the same time, the mechanical shutter 24 is opened, and light corresponding to the subject is transmitted through the lens 21 to each of the photoelectric conversion elements 31 of the MOS type imaging element 30. Is incident on. At this time, all the photoelectric conversion elements 31
Since the potentials of the upper gate electrode 41 and the drain electrode 37 are set to 0 (V) and the lower gate electrode 33 is set to -20 (V) for the accumulation of holes, the light reception of each photoelectric conversion element 31 is performed. The holes generated in accordance with the amount of light thus accumulated are accumulated in each semiconductor thin film 35. Thereafter, the mechanical shutter 24 closes immediately. Next, the drain driver 48
Each signal line 44 is turned on by an ON signal from the data selector 49.
After a voltage of a predetermined value is precharged and a drain voltage of 10 (V) is applied to the drain electrode 37 of the photoelectric conversion element 31, the switching element Q is opened by an off signal from the data selector 49. Then, data is sequentially detected from the photoelectric conversion elements 31 in the first row of each photoelectric conversion element 31. -20 from the upper gate driver 52 is applied to the upper gate electrode 41 of the photoelectric conversion element 31 in the first row.
(V) signal voltage Vt is applied and the lower gate electrode 33
, A signal voltage Vb of 10 (V) from the lower gate side driver 42 is applied, and the photoelectric conversion elements 31 in the first row are in a selected state. Each signal line 44 has a data selector 49
10 (V) from the drain driver 48 by the ON signal of
The state where the signal voltage Vd is charged continues. At the same time, the upper gate electrode 41 and the lower gate electrode 33 of the photoelectric conversion element 31 in the second row to the last row have a potential of 0 (V) and a lower gate electrode 33 of −
The state where holes are accumulated in a non-selective manner while 20 (V) is applied continues. In the photoelectric conversion element 31 in the first row, holes accumulated according to the amount of light are localized by the gate voltage Vt of the upper gate electrode 41 and cancel the gate voltage Vt, so that an n-channel is generated and the drain current is reduced. Then, the potential of the signal line 44 is discharged in accordance with the amount of light. First
The voltage discharged by the photoelectric conversion element 31 in the row is taken into the drain driver 48 in a state where the switching element Q is closed by the ON signal of the data selector 49. The drain driver 48 outputs to the output terminal Vout an electric signal Se obtained by amplifying the fetched data voltage by an internal buffer circuit. Subsequently, the photoelectric conversion elements 31 in the second row are selected as described above, the photoelectric conversion elements 31 in the first row and the third and subsequent rows are deselected, data is taken in, and the electric signal Se for one screen is output. Output for each line. Then, similarly to the monitoring mode, the electric signal Se for one frame that has been finally transferred is the sample fold circuit 53, the A / D converter 54, and the color process circuit 57.
Is converted to YUV data via The CPU 61 reads out the YUV data in a predetermined format via the DMA controller 58, and inputs the YUV data to the image compression / expansion circuit 62 for compression. The compressed data is stored in a recording memory 6.
Stored as 0. After this storage is completed, the CPU 61 sets the timing generator 56 and the color process circuit 57
Again to automatically return to monitoring mode.

In the reproduction mode, the key input units 12a, 12a
b, 12c, and 12d, the recording memory 6
The compressed data stored at 0 is decompressed by the image compression / decompression circuit 62, and one frame of the decompressed YUV data is read from the image compression / decompression circuit 62 and written to the VRAM 64 via the VRAM controller 63. VRA
One frame of YUV data written to M64 is
The digital video encoder 65 reads and converts the data in a line-sequential manner, and outputs the analog video signal Sa to the display unit 10. In addition, it may be set so that the mode is switched to the reproduction mode immediately after the end of shooting in the image recording mode, and the display unit 10 displays an image of one frame shot.

In the digital still camera according to the present embodiment, the MOS type image pickup device 30 can perform highly sensitive detection even with short-time irradiation of weak light (by applying an offset bias to the upper gate electrode 41). Therefore, even when light of dark illuminance is incident on the lower MOS transistor having the lower gate electrode 33 as a gate, photoelectric conversion can be performed by flowing a drain current into this channel. By opening and closing the mechanical shutter 24, an image can be taken instantaneously, and display data with less blur can be obtained. In particular, high-precision shooting can be performed for fast-moving subjects and for applications such as reading originals. As described above, in the present embodiment, a digital still camera capable of high-definition photographing can be provided by using the MOS imaging device 30 manufactured using the TFT process technology.

Although the embodiments have been described above, the present invention is not limited to the embodiments, and various changes accompanying the gist of the configuration are possible. For example, in the above-described embodiment, a mechanical shutter is applied as a high-speed shutter, and the exposure time of the MOS type image sensor 30 is made substantially the same. However, a polymer dispersed liquid crystal cell or other various liquid crystal cells may be used as the shutter. Good. In this case, there is an advantage that the light exposure from all the pixels can be performed simultaneously since all the pixels can simultaneously receive light from the subject side and can simultaneously block light in all the pixels.

[0034]

As is apparent from the above description, according to the present invention, it is possible to use a MOS type image pickup device manufactured using a thin film technology, and it is possible to capture a high-definition image of 5 million pixels or more. It is possible to realize a digital still camera capable of realizing a practical image capturing speed.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a digital still camera according to the present invention.

FIG. 2 is an explanatory cross-sectional view of an imaging unit of the digital still camera according to the embodiment.

FIG. 3 is a cross-sectional view showing a photoelectric conversion unit of the MOS type imaging device used in the embodiment.

FIG. 4 is a circuit diagram of a MOS type imaging device used in the embodiment.

FIG. 5 is a block diagram showing a circuit configuration of the digital still camera according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Camera main body part 2 Imaging part 10 Display part 21 Lens 24 Mechanical shutter 30 MOS type imaging element 31 Photoelectric conversion part 33 Lower gate electrode 34 Lower gate insulating film 35 Semiconductor thin film 36 Source electrode 37 Drain electrode 40 Upper gate insulating film 41 Upper gate electrode

Continued on the front page F term (reference) 2H054 AA01 4M118 AA10 AB01 BA14 CA11 CB06 FA06 HA19 5C022 AA13 AB17 AC03 AC31 AC32 AC42 AC52 AC54 AC69 AC73 AC77 5C024 AA01 BA01 CA11 CA12 DA01 DA02 DA04 DA07 EA04 FA01 FA11 GA02 GA31 HA06 HA12

Claims (4)

[Claims] 1. A MOS type image sensor in which a plurality of photoelectric conversion units each composed of a MOS type photo sensor having upper and lower gate electrodes are arranged in a matrix, and an optical element for forming an image of a subject on a light detection surface of the MOS type image sensor. A digital still camera, comprising: a system; and a shutter for exposing a light detection surface of the MOS type imaging device for a predetermined time. 2. The semiconductor device according to claim 1, wherein the photoelectric conversion unit comprises a semiconductor layer having a-Si and a gate opposed to the semiconductor layer via a gate insulating film on both sides of a source and a drain provided on the semiconductor layer. 2. The digital still camera according to claim 1, wherein an electrode is provided, a sense gate bias and a reset bias are applied to the one gate electrode, and a read selection signal is supplied to the other gate electrode. 3. The digital still camera according to claim 1, wherein all of the photoelectric conversion units constituting the MOS type imaging element simultaneously take in light for a predetermined time when the shutter is opened and closed. 4. The digital still camera according to claim 1, wherein said shutter is a mechanical shutter.