JPH06216359A - Photosensor system - Google Patents

Abstract

PURPOSE:To provide a photosensor system having a sensor function and a selection transistor function and a high density arrangement set up by connecting in series photosensors in the direction of a signal line. CONSTITUTION:The bottom gate electrode of each sensor 1 is formed on an insulative substrate, and covered with a bottom gate insulating film. Thereon a semiconductor layer is formed, and a source electrode (S) and a drain electrode (D) are formed so as to sandwich the semiconductor layer. These are covered with a top gate insulating film, on which a top gate electrode (TG) is formed in a facing position to the bottom gate electrode (BG). The source electrode (S) and the drain electrode (D) of each photosensor 1 in the direction of a signal line are connected in series. When a top gate voltage VTG is controlled to be 0 [V] and -20 [V], a sense state and a reset state can be controlled. When a bottom gate voltage VBG is controlled to be 0 [V] and +10 [V], a selection state and a non-selection state can be controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a photosensor system, and more specifically, a photosensor having a sensor function and a selection transistor function is connected in series to one photosensor to achieve high density. The present invention relates to a photo sensor system.

[0002]

2. Description of the Related Art Conventionally, photosensor systems are usually
Photodiodes and TFTs (Thin Film Transistors) are used as light receiving elements (photosensors), and a plurality of photosensors are arranged in a matrix. Then, each photosensor generates an electric charge according to the amount of the emitted light, and the luminance can be known by observing the amount of the electric charge. A scanning voltage is applied from the horizontal scanning circuit and the vertical scanning circuit to the photosensors arranged in a matrix to detect the charge amount of each photosensor.

However, in the conventional photosensor, when a closed circuit is formed, the generated charge is discharged as a current. Therefore, conventionally, a selection transistor is formed separately from the photosensor and connected to each photosensor. Then, by driving the selection transistor by the horizontal scanning circuit and the vertical scanning circuit, the charge amount of each photosensor is detected.

[0004]

However, in such a conventional photosensor system, since the selection transistor is formed and connected for each photosensor, each photosensor cell becomes large, and the photosensor system becomes large. There is a problem that the device itself becomes large and becomes an obstacle to high density of pixels.

Therefore, according to the present invention, the photosensor itself has a photosensor function and a selection function, and the source electrode and the drain electrode of the photosensor are connected in series for each signal line, whereby the conventional selection transistor is selected. It is an object of the present invention to provide a photo sensor system that can be made smaller and the photo sensor cell can be made smaller, and the photo sensor system itself can be miniaturized to increase the density of pixels.

[0006]

In a photosensor system of the present invention, a source electrode and a drain electrode are arranged to face each other with a semiconductor layer sandwiched therebetween, and the semiconductor layer, the source electrode and the drain electrode are sandwiched with both sides thereof. A first gate electrode and a second gate electrode facing the semiconductor layer via an insulating film, respectively, and one of the first gate electrode side and the second gate electrode side is a light irradiation side, and A photosensor system comprising a plurality of photosensors, wherein light emitted from the light irradiation side is transmitted through an insulating film on the light irradiation side and is irradiated to the semiconductor layer, wherein The source electrode and the drain electrode of adjacent photosensors arranged along the line are connected in series, and the voltage applied to the light irradiation side gate electrode of each photosensor is controlled to control the voltage of the photosensor. Sense state control means for controlling the sense state of the sensor and a voltage applied to a gate electrode facing the light irradiation side gate electrode of each photosensor are controlled to control the selected and non-selected states of the photosensor. The above-mentioned object is achieved by the selection control means.

Further, the source electrode or the drain electrode of the photosensor connected in series is connected in series,
The above object is achieved by providing selection means for turning on / off the output of the photosensors connected in series.

In each of the above cases, the sense state control means may control, for example, the voltage applied to the gate electrode on the light irradiation side to control the set and reset states of the photosensor. .

[0009]

In a photosensor system including such a photosensor, source electrodes and drain electrodes of adjacent photosensors arranged along the signal line among the plurality of photosensors are connected in series, and The voltage applied to the light irradiation side gate electrode arranged on one side of the semiconductor layer is controlled to control the sense state of the photosensor, and the voltage applied to the gate electrode of each photosensor is controlled. Since the selection and non-selection states of the photosensor are controlled, the photosensor can have both the function as a photosensor and the function as a selection transistor. The selection transistor for selecting the sensor can be removed, and the source electrode and drain of the photosensor adjacent to each other along the signal line can be removed. Since the series connecting electrode, it is possible to reduce the wiring area and connection points. As a result, the photo sensor system itself can be downsized, and the density of pixels can be increased.

Also, the source electrode or the drain electrode of the photosensors connected in series is connected in series,
Since the selection means for turning on / off the outputs of the photosensors connected in series is provided, even when a plurality of photosensors are arranged in a matrix, by turning on / off the selection means, the data line It is possible to easily take out the output of the photo sensor for each time.

Furthermore, since the voltage applied to the gate electrode on the light irradiation side is also controlled to control the set and reset states of the photosensor, the previous accumulated charge can be immediately discharged, and the light irradiation amount can be continuously changed. Can be detected.

[0012]

EXAMPLES The present invention will be described below based on examples.

1 to 5 are views showing an embodiment of a photo sensor system, FIG. 1 is a side sectional view of a photo sensor used in the photo sensor system, and FIG. 2 is FIG.
4 is an equivalent circuit of the photosensor of FIG. 3, FIG. 3 is an explanatory diagram of a voltage applied to each electrode of the photosensor of FIG.
3 is a characteristic curve diagram showing the output characteristic in the voltage application state of FIG. 3, and FIG. 5 is an equivalent circuit diagram showing a part of an example of a sensor array to which a photo sensor is applied.

In FIG. 1, the photosensor 1 basically has a structure in which an inverted stagger type thin film transistor and a coplanar type thin film transistor are combined into a single semiconductor layer.

That is, the phototransistor 1 has a structure in which chromium (Cr) is formed on a transparent insulating substrate 2 made of glass or the like.
Is formed, and a bottom gate insulating film 4 made of silicon nitride (SiN) is formed so as to cover the bottom gate electrode (BG) 3 and the insulating substrate 2. This bottom gate insulating film 4
May use Si-rich Si _x N _1-x having a Si / N composition ratio larger than “1”.

On the bottom gate electrode (BG) 3,
A semiconductor layer 5 is formed at a position facing the bottom gate electrode (BG) 3, and the semiconductor layer 5 is formed of i-type amorphous silicon (ia-Si). A source electrode (S) 6 and a drain electrode (D) 7 made of chromium (Cr) or the like are formed on the semiconductor layer 5 so as to sandwich the semiconductor layer 5 and to face each other at a predetermined distance. The source electrode (S) 6 and the drain electrode (D)
7 is connected to the semiconductor layer 5 via n ⁺ silicon layers 8 and 9 made of amorphous silicon in which a dopant such as phosphorus is diffused. These form a bottom transistor (inverse staggered thin film transistor) BTr.

A portion of the semiconductor layer 5 between the source electrode (S) 6 and the drain electrode (D) 7 and between the source electrode (S) 6 and the drain electrode (D) 7 of the semiconductor layer 5 is a top gate insulation made of transparent silicon nitride. The top gate insulating film 10 is covered with the film 10 and the bottom gate electrode (B
A top gate electrode (TG) 11 made of a transparent conductive material is formed at a position opposite to G) 3. The top gate electrode (TG) 11 is not limited to the channel region of the semiconductor layer 5 in order to generate electron-hole pairs, which will be described later.
As shown in FIG. 1, it is desirable that the n ⁺ silicon layers 8 and 9 are formed to have a size that also covers the upper surfaces. Although not shown, a transparent overcoat film made of silicon nitride is formed so as to cover and protect the top gate electrode (TG) 11 and the top gate insulating film 10.
The top gate electrode (TG) 11, the top gate insulating film 10, the semiconductor layer 5, the source electrode (S) 6 and the drain electrode (D) 7 form a top transistor (coplanar thin film transistor) TTr.

In this embodiment, this photosensor 1 is irradiated with irradiation light A from the side of the top gate electrode (TG) 11 as shown in FIG. 1, and this irradiation light A is applied to the top gate electrode (TG) 11 and Through the top gate insulating film 10,
The semiconductor layer 5 is irradiated. Note that the photosensor 1 is not limited to the one that irradiates the irradiation light A from the top gate electrode 1 side, as is apparent from the above configuration.
Even if irradiation is performed from the bottom gate electrode (BG) 3 side, the operations described below can be similarly performed.

In this photosensor 1, for example, the bottom gate electrode (BG) is 1000 ‰ (angstrom),
The bottom gate insulating film 4 is 2000 ‰, and the semiconductor layer 5 is 15
00 ‰, the source electrode (S) and the drain electrode (D) are 5
00 ‰, the ohmic contact layers 8 and 9 are 250 ‰, the top gate insulating film 10 is 2000 ‰, and the top gate electrode (T
G) is formed at 500% and the overcoat film is formed at 4000%, and the distance between the source electrode (S) and the drain electrode (D) on the semiconductor layer 5 is formed at 7 μm.

As described above, the photosensor 1 has a structure in which the inverse stagger type thin film transistor BTr and the coplanar type thin film transistor TTr are combined, and an equivalent circuit thereof can be shown as in FIG.

Next, the operation of the photo sensor 1 will be described.

As shown in FIG. 3, the photosensor 1 controls the voltage applied to the bottom gate electrode (BG) and the voltage applied to the top gate electrode (TG) to select a selected state, a non-selected state and a sense state. The state and the reset state can be controlled.

That is, as shown in FIGS. 3C and 3D, when a positive voltage, for example, +10 [V] is applied to the bottom gate electrode (BG) of the photo sensor 1, the semiconductor layer 5 is n-channel. Is formed. Here, a positive voltage between the source electrode (S) and the drain electrode (D), for example, +1
When 0 [V] is applied, electrons are supplied from the source electrode (S) side and a current flows. In this state, as shown in FIG. 3D, if a negative voltage of a level such that -20 [V] is erased to the top gate electrode (TG) by the electric field of the bottom gate electrode (BG), the n channel is extinguished. The electric field from the top gate electrode (TG) acts in a direction to reduce the influence of the electric field from the bottom gate electrode (BG) on the channel layer. As a result, the depletion layer extends in the thickness direction of the semiconductor layer 5 and pinches off the n channel. At this time, when the irradiation light A is irradiated from the top gate electrode (TG) side,
Electron-hole pairs are induced on the top gate electrode (TG) side of the semiconductor layer 5. However, the top gate electrode (TG)
Since −20 [V] is applied, the induced holes are accumulated in the channel region and cancel the electric field of the top gate electrode (TG). Therefore, an n-channel is formed in the channel region of the semiconductor layer 5 and a current flows. Then, the source electrode (S) - drain electrode (D) flowing between the current (hereinafter drain current) I _DS, depending on the number of holes induced by irradiated light A, i.e. corresponding to the amount of illumination light A Change.

As described above, in the photo sensor 1, the electric field from the top gate electrode (TG) is applied to the bottom gate electrode (B).
G) is controlled so as to work against the channel formation due to the electric field from G) and pinches off the n channel, so that the drain current I _DS flowing during no light irradiation is extremely small, for example, 10 ^−14. It can be about A (ampere). As a result, the photosensor 1 can sufficiently increase the difference between the drain current I _DS during light irradiation (bright time) and the drain current I _DS during no light irradiation (dark), and the bottom at this time. The amplification factor of the transistor changes depending on the amount of irradiated light, so that the S / N ratio can be increased.

In the photo sensor 1, as shown in FIG. 3C, a positive voltage (+1) is applied to the bottom gate electrode (BG).
0 [V]) is applied, the top gate electrode (T
When G) is set to 0 [V], for example, holes can be discharged from the trap level between the semiconductor layer 5 and the top gate insulating film 10 for refreshing, that is, resetting. That is, when the photosensor 1 is continuously used, the trap levels between the top gate insulating film 10 and the semiconductor layer 5 are holes generated by light irradiation and holes injected from the drain electrode (D). The channel resistance in the non-illuminated state becomes smaller,
The drain current I _DS increases when there is no light irradiation. Therefore, 0 [V] is applied to the top gate electrode (TG) to discharge the holes and reset.

Further, as shown in FIGS. 3 (A) and 3 (B), the photo sensor 1 has a bottom gate electrode (BG).
In addition, when a positive voltage is not applied, a channel is not formed in the semiconductor layer 5, and the drain current I _DS does not flow even if light irradiation is performed, so that a non-selected state can be obtained. That is, the photo sensor 1 has a bottom gate electrode (BG).
It is possible to control the selected state and the non-selected state by controlling the voltage (hereinafter, bottom gate voltage) V _BG applied to the gate. Further, in this non-selected state, FIG.
As shown in (A), 0 is applied to the top gate electrode (TG).
When [V] is applied, holes can be discharged from the trap level between the semiconductor layer 5 and the top gate insulating film 10 and reset as in the above.

Next, a drain current characteristic curve when the voltage applied to the top gate electrode (TG) (hereinafter referred to as the top gate voltage) V _TG is changed is shown for the operation in the selected state among the above operations. This will be described with reference to FIG. In addition, as shown in FIGS. 3C and 3D, FIG.
The characteristic of the drain current I _DS when the top gate voltage V _TG is changed with the light amount of the irradiation light A as a parameter is shown with +10 [V] being applied as the bottom gate voltage V _BG .

That is, in the state shown in FIGS. 3C and 3D, when the irradiation light A having a light amount of 2300 lux (lx) is irradiated, as shown by the drain current characteristic curve T1 in FIG. Even if the top gate voltage V _TG changes, a drain current I _DS of 1 μA (microampere) or more always flows. When the irradiation light A having a light amount of 400 lux is irradiated, as shown by the drain current characteristic curve T2 in FIG. 4, when the top gate voltage V _TG is between 0 [V] and -12 [V], it is 1 μA. When the above-mentioned drain current I _DS flows and the top gate voltage V _TG exceeds −12 [V], the drain current I _DS is somewhat reduced,
A current of 0.1 μA or more always flows. That is, 40
In the bright time when the irradiation light A having a light amount of 0 lux (lx) or more is irradiated, a drain current I _{DS of} 0.1 μA or more always flows.

Similarly, FIG. 3 (C) and FIG. 3 (D)
In the state shown in (1), when the light amount is 1 lux, as shown by the drain current characteristic curve D1 in FIG. 4, when the top gate voltage V _TG is 0 [V], the drain current I _DS of 1 μA or more flows, Top gate voltage V _TG is -12
When the voltage becomes lower than [V], the drain current I _DS sharply decreases, and when the top gate voltage V _TG becomes -16 [V] or lower, the drain current I _DS becomes 1 pA (picoampere) or lower. Further, when the light amount is 16 lux, as shown by the drain current characteristic curve D2 in FIG. 4, when the top gate voltage V _TG is 0 [V], the drain current I _DS of 1 μA or more flows, but the top gate voltage V _TG flows. V _TG is -12
When it becomes lower than [V], it rapidly decreases, and when the top gate voltage V _TG becomes -17 [V] or lower, the drain current I
_DS will be less than 1 pA.

Therefore, as shown in FIG. 3, the photosensor 1 sets the top gate voltage V _TG to 0, for example.
By controlling to [V] and −20 [V], the drain current I _DS changes to a value of 1 μA or more and a value of 1 pA or less during non-irradiation (dark), and the top gate voltage V _TG
Is set to −20 [V], the drain current I
_DS is 1 pA when no light is radiated and 1 when light is radiated
It can be μA or more. As a result, by controlling the top gate voltage V _TG to 0 [V] and -20 [V], the sense state and the reset state can be controlled, and the drain during light irradiation and during no light irradiation can be controlled. Current I
_{The DS} ratio is 10 ⁶ times or more, and the irradiation amount of the irradiation light A is S
It is possible to read with a high sensitivity of 120 dB or more in / N ratio. In addition, the bottom gate voltage V _{BG is set} to 0 [V], for example.
And +10 [V], the selected state and the non-selected state can be controlled. As a result, by controlling the top gate voltage V _TG and the bottom gate voltage V _BG , the photosensor 1 itself operates as having both a function as a photosensor and a function as a selection transistor. You can

Therefore, when the photosensor 1 is applied to a sensor array, it is utilized that the photosensor 1 has both a function as a photosensor and a function as a selection transistor as shown in FIG. 1
The photosensors 1 on the data line are connected in series and used.

That is, when applied to a sensor array,
A large number of photosensors 1 are arranged in a matrix, and each photosensor 1 is adjacent to each data line (signal line) thereof.
The source electrode (S) -drain electrode (D) is connected in series, and the bottom gate electrode (BG) is connected in common to form a so-called NAND structure. Then, the source electrode (S) of the final-stage photosensor 1 connected in series is grounded, and the column switch 20 is connected to the drain electrode (D) of the first-stage photosensor.
The column switch 20 may be of any type as long as it has a simple switch characteristic.

In such a structure, as described above,
Top gate voltage V of each photosensor 1 connected in series
By controlling _TG , the selected state and non-selected state of each photosensor 1 can be controlled, and by controlling the bottom gate voltage V _BG at that time, the sense state and the reset state can be controlled. You can

That is, the data line is selected by the bottom gate voltage V _BG , the photosensors 1 of the data line are sequentially sensed by the top gate voltage V _TG , and the column switch 20 is turned on to make the selection. The output of each photosensor 1 on the data line can be sequentially taken out via the column switch 20.

In this case, the photosensors 1 connected in series
Has a resistance value obtained by multiplying the number of photosensors 1 connected in series (4 in the case of FIG. 5) by the internal resistance value of the photosensor 1. As can be seen from the values of the drain current I _DS shown in FIG. 4 described above, the sensor 1 has an internal resistance whose top gate voltage V _TG is 0 [V] at the time of reset or light irradiation (light). Is about 10 megohms (MΩ), whereas it is 10 teraohms (T) when there is no light (dark).
Ω), the ratio of the internal resistance of the selected photosensor 1 in the bright and reset states to the internal resistance in the dark state is 10 ⁶ times. Therefore, the light irradiation amount of the photo sensor 1 _sensed by the top gate voltage V _TG can be read with high sensitivity of 120 dB or more.

As described above, since the photo sensor 1 itself has both the function as a photo sensor and the function as a selection transistor, a selection transistor for selecting a conventional separately formed photo sensor is provided. Besides, the source electrode and the drain electrode of the photosensors adjacent to each other along the signal line are connected in series, so that the wiring area and the number of connection points can be reduced. As a result, the photo sensor system itself can be downsized, and the density of pixels can be increased.

In FIG. 5, only four photosensors 1 are connected in series for simplification of description, but the number of photosensors is not limited to this, and the number of photosensors used in a normal sensor array is not limited thereto. 1 can be connected in series to obtain a sufficiently high-sensitivity output, for example, 10,000 photosensors 1
Even if they are connected in series, the total internal resistance of the photosensor 1 during light irradiation or in the reset state is 10 ⁵ MΩ (10 ⁴ × 1
0 = 10 ⁵ MΩ), and photosensor 1 when there is no light irradiation.
Since the ratio with the internal resistance of 10 is 10 2, a sensitivity of 40 dB can be obtained.

[0038]

According to the photo sensor system including such a photo sensor, the source electrode and the drain electrode of the photo sensors adjacent to each other arranged along the signal line among the plurality of photo sensors are connected in series. The sense state of the photosensor is controlled by controlling the voltage applied to the gate electrode on the light irradiation side which is connected to the semiconductor layer and is disposed on one side of the semiconductor layer, and is applied to the gate electrode of each photosensor. The voltage is controlled to control the selected and non-selected states of the photosensor. Therefore, the function as a photosensor and the function as a selection transistor can be provided at the same time, and a selection transistor for selecting a photosensor which is separately formed and arranged in the related art can be removed and a signal line can be removed. Since the source electrode and the drain electrode of the photosensors adjacent to each other are connected in series, the wiring area and the number of connection points can be reduced. As a result, the photo sensor system itself can be downsized, and the density of pixels can be increased.

Furthermore, since the voltage applied to the gate electrode on the light irradiation side is also controlled to control the set and reset states of the photosensor, the previous accumulated charge can be immediately discharged, and the light irradiation amount can be continuously changed. Can be detected.

[Brief description of drawings]

FIG. 1 is a front sectional view of a photo sensor applied to an embodiment of a photo sensor system according to the present invention.

FIG. 2 is an equivalent circuit of the photo sensor of FIG.

FIG. 3 is an explanatory diagram of a voltage applied to each electrode of the photosensor of FIG. 1 and a state change thereof.

FIG. 4 is a characteristic curve diagram showing characteristics of drain current when the top gate voltage is changed with the light irradiation amount as a parameter.

5 is an equivalent circuit diagram showing a part of an example of a sensor array to which the photo sensor of FIG. 2 is applied.

[Explanation of symbols]

1 Photosensor 2 Insulating Substrate 3 Bottom Gate Electrode (BG) 4 Bottom Gate Insulation Film 5 Semiconductor Layer 6 Source Electrode (S) 7 Drain Electrode (D) 8, 9 n ⁺ Silicon Layer 10 Top Gate Insulation Film 11 Top Gate Electrode (TG) 20 Column switch

Claims (3)

[Claims] 1. A source electrode and a drain electrode are arranged so as to face each other with a semiconductor layer interposed therebetween, and the semiconductor layer, the source electrode and the drain electrode are opposed to the semiconductor layer with an insulating film interposed therebetween on both sides thereof. A first gate electrode and a second gate electrode facing each other, and the first gate electrode side or the second gate electrode side
One of the gate electrode sides is a light irradiation side, and a photo is provided with a plurality of photosensors in which light emitted from the light irradiation side is transmitted through an insulating film on the light irradiation side and is irradiated to the semiconductor layer. A sensor system, wherein a source electrode and a drain electrode of adjacent photosensors arranged along a signal line among the plurality of photosensors are connected in series, and a gate on a light irradiation side of each photosensor. Sense state control means for controlling the voltage applied to the electrodes to control the sense state of the photosensor, and controlling the voltage applied to the gate electrode facing the light irradiation side gate electrode of each photosensor by controlling the voltage A photo sensor system comprising: a selection control unit that controls a selected or non-selected state of the photo sensor. 2. A selection means, which is connected in series to a source electrode or a drain electrode of the photosensors connected in series and which turns on / off the output of the photosensors connected in series, is provided. Photo sensor system. 3. The photo according to claim 1, wherein the sense state control means controls the voltage applied to the gate electrode on the light irradiation side to control the set and reset states of the photosensor. Sensor system.