JPS62149251A - Image sensor - Google Patents

Abstract

PURPOSE:To remarkably facilitate the manufacture by functioning one of thin film transistors (TRs) as a photodetector for a prescribed time and holding the other in the conducting state during the time so as to suppress the increase in output conduction lead wires thereby decreasing number of components on a substrate. CONSTITUTION:An optical switch P consists of two thin film TRs FETT1, T2 connected in series. In giving a gate voltage to the TR FETT2 only, the TR is turned on as a switching element but the TR FETT1 keeps the off-state. In irradiating a light to the channel of the TR T1 in the off-state, the entire sensor P is turned on. That is, the TR FETT1 acts like a photodetector and the sensor P is turned on or off depending only on the presence of the light sensing. Thus, in opening an analog switch A, the presence of the photodetection of the TR FETT1 is converted into the presence of a current flowing to ground from a DC power supply 4 via the sensor P, the switch A and a resistor 7 and represents the presence of the output of an amplifier 8. In giving a gate voltage to the TR FETT1 only conversely, the TR FETT2 acts like a photodetector and the similar detection is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an image sensor used in facsimiles and the like.

[Prior Art and its Problems] In a conventional image sensor, a lead wire for guiding an output signal to an external circuit is provided for each optical sensor (for example, a photodiode) forming a line sensor. For this reason, the amount of work for connecting the lead wires (performed by wire bonding, etc.) increases, which has been a problem in manufacturing.

For this reason, in recent years, devices have been developed in which the output signals from each of the optical sensors are guided to an external circuit in a time-division manner, and the number of lead wires is reduced, for example, as shown in FIG. 7.

In FIG. 7, 64 photodiodes S1.1 to S58.8 making up the licensor 2 and a scanning circuit 3 for time-division processing are connected to the photodiodes in a one-to-one relationship. 64 thin film transistors inch T1. ．． -T8.8 is divided into 8 groups of 8 pieces each. The gates of the thin film transistor switches in each group are connected to the same scanning signal line for each group, and are turned on and off for each group. That is, the photodetection signals obtained by the 64 photodiodes are divided into groups and sent to the external circuit 5 in a time-sharing manner as 8-bit parallel signals.

However, with this type of device, although it is possible to reduce the number of lead wires led out from the board on which the line sensor is configured, there are many photodiodes that make up the line sensor on the same board, and the same number of lead wires. There is a problem in that it is necessary to form switching elements and Buttrix wiring to connect them, which makes the manufacturing process extremely complicated.

[Object of the invention 1 This invention was made based on the above-mentioned circumstances,
The purpose of this is to reduce the number of elements formed on the board while minimizing the increase in the number of lead wires that lead the output from the board on which the line sensor is formed to the external circuit. The object of the present invention is to provide an image sensor that is significantly easier to manufacture.

[Main points of IJ] In order to achieve the above-mentioned object, the present invention has a conductive state when a gate voltage is applied and when the channel section receives light (i.e., a switching function and a photodetector plow). A photosensor is configured by connecting a plurality of thin film transistors in series, and one of the plurality of thin film transistors is sequentially operated as a photodetecting element without applying a gate voltage for a certain period of time. let me,
During this time, the gate voltage was continued to be applied to the other thin film transistors to keep them conductive.

[Example] First, before explaining this example, the principle of an optical sensor, which is the basic unit of the configuration in this example, will be explained in terms of I/X.

FIG. 1 focuses on one photosensor P and shows the relationship between this and the DC power supply 4 and other circuits. As shown in the figure, the optical sensor P is composed of thin film transistors T+, which are two N-channel MO5@FETs connected in series,
T2 (the source of the Q film transistor TI and the drain of the thin film transistor T2 are connected). And these thin film transistors TI, T2
are amorphous silicon MO3-FE with the same function.
T, and becomes conductive when the channel portion receives light or when a voltage is applied to the gate. That is, the thin film transistors T+ and T2 have both a photodetection function and a switching contact.

Now, in a circuit as shown in FIG. 1, if a gate voltage is applied only to the thin film transistor T2 of the photosensor P, the thin film transistor T2 as a switching element turns on, but the thin film transistor T+ remains on. but,
Here, off-state! When light is applied to the channel portion of the thin film transistor TI located at 3, the thin film transistor T1 also becomes conductive, and the optical sensor P as a whole also becomes conductive. That is, in this case, the thin film transistor T1 works as a photodetecting element, and the photo sensor P becomes conductive or nonconductive depending only on whether or not it receives light. Therefore, when the analog switch A is opened, the thin film transistor TI detects light. The presence or absence of this indicates the presence or absence of current flowing from the DC type TA4 to the ground via the optical sensor P, analog switch A, and resistor 7.
Furthermore, this is detected as the presence or absence of the output of the amplifier 8.

In the end, the presence or absence of light reception by the thin film transistor T1, to which no voltage is applied to the gate, indicates the presence or absence of an output from this circuit. Conversely, when a gate voltage is applied only to the ss transistor T1, the thin film transistor T2 acts as a photodetecting element, contrary to the above case, and the presence or absence of light reception is detected as the presence or absence of an output from this circuit.

For this reason, the gate '
After applying a tonnage pressure and turning it on, the first half of T/
2, the gate voltage is applied only to the Q film transistor T2, and during the latter half T/2, the gate voltage is applied only to the thin film transistor T2.
If a gate voltage is applied only to transistors T1 and T2, the thin film transistors T, , T2
The photodetection signal at is sent to the amplifier 8 as a serial signal.

In other words, depending on the timing of one thin film transistor,
It is used as a switching element or a photoanalyzer to send each photodetection signal to the analog switch A and the amplifier 8 in a time-division manner.

Note that the optical sensor P in FIG. 1 is made up of two thin film transistors connected in series, but this is replaced by a number of Q film transistors connected in series, selectively leaving only one of them. If a gate voltage is applied to all the others, only one of them will act as a photodetector and the others will remain conductive, so no gate voltage will be applied! I! By sequentially changing the nine transistors, it becomes possible to grasp the optical information at the position of the thin film transistor each time.

Next, the structure of the optical sensor P shown in FIG. 1 will be explained based on FIG. 2. Insulated MOS − on the glass substrate 20
Thin film transistors TI and T2, which are FETs, are formed using integrated circuit technology. The gate electrode 21 is made of a thin film of molybdenum or chrome, for example, and a silicon oxide film is formed as an insulating layer 22 above it. Furthermore, an amorphous silicon layer 23 and an aluminum electrode 24 are disposed above it. A drain 25 and a source 26 doped with phoscine (PH3) to form an N-type amorphous semiconductor are formed on the upper surface side of the amorphous silicon layer 23 at the boundary with the electrode 24. In addition,
F! The source 26 of the film transistor T1 is connected to the drain 25 of the thin film transistor T2 through an electrode 24, and both thin film transistors are connected in series.

FIG. 3 is a circuit diagram of this embodiment. A licensor 2 consisting of the above-mentioned optical sensors P+, P2, . . . The circuit IO detects output signals from the line sensor 2 and uses them as image signals.

That is, n optical sensors P described above are connected in parallel between the DC power supply 4 and the detection circuit 10.

And each of these n photosensors P,, P2,...
...P, the left thin film transistor T+, +
, T2. The gates of Tn, 1, . On the other hand, the right thin film transistors TI 2 , T2.2 , . . . Tn,
Since the gates of the thin film transistors 2 and 2 are collectively connected to the control signal lower signal line, when the control signal becomes H (high), these thin film transistors are all turned on.

Moreover, the analog switch AI of the multiplexer 11,
A2. =...An is the sample signal S1. 'S2...
... Optical sensor PI, P2 that receives and connects Sn
. . . The photodetection signals from P are sent to the amplifier 8 in a time-division manner.

Next, the operation in this implementation will be explained. First, the control signal φ
, φ and sample signal Sl , 52...Sn
Explain the relationship between The control signal φ and the bottom are rectangular waves with a period T as shown in FIG. 4, and the control signal 7 is an inverted signal of the control signal φ. On the other hand, as shown in FIG. 4, the sample signals S, , S2...Sn rise in synchronization with the rise of the control signal j, have a pulse width equal to the control signal φ, and have the same period as the period T below. It is something to do. For this reason, for example, if the sample signal S is applied to the analog switch A1,
+ is sent and the analog switch A1 turns on, and this on state continues at T/2 (4th UI!) of the first half of T.
At timing l) at J, the control signal i is H, so the thin film transistor T1.2 becomes conductive, and the left 61 film transistor T1.2 acts as a photodetector. , is receiving light, the thin film transistor T1. 1, T1.2 and the analog switch AI are both conductive and the output is sent to the amplifier 8, but the thin film transistors T1. Output is not sent unless I is receiving light, and T/2 in the second half
(At timing 2), since the control signal φ is H, the thin film transistor T1,1 becomes conductive, and if the right thin film transistor T1.2, which acts as a photodetecting element, is receiving light, then the thin film transistor T1,1 becomes conductive.
The simulated transistors T+, +, T1.2 and the analog switch A1 are both conductive and the output is sent to the intensifier 8, but no output is sent if the thin film transistor TI2 is not receiving light. Below, the analog switch f-
A2. A3... Sample signals S2, S to An
3...Similar operations are sequentially performed when Sn is sent. That is, the photodetection signals at the positions of the 2n thin film transistors are sent to the amplifier 8 as a 2n-bit serial signal.

As described above, in this embodiment, in a licensor formed by arranging n optical sensors connected in parallel, the optical sensor is replaced by a thin film transistor that becomes conductive when a gate voltage is applied and when the channel part receives light. In each optical sensor, any one of the plurality of thin film transistors is sequentially operated as a photodetecting element without applying a gate voltage for a certain period of time, During that time, I applied gate voltage to the other thin film transistors to keep them conductive.
The number of elements formed on the substrate can be halved compared to the conventional example (shown in FIG. 7) while suppressing a large increase in the number of Riet wires that lead the output from the licensor 2 to the detection circuit 10. It becomes possible to greatly facilitate the production of.

Next, other embodiments will be described. A circuit diagram of the image sensor according to this embodiment is shown in FIG.

Parallel on board l! 1i unified n photosensors PI,
This is the same as the previous embodiment in that the licensor 2 is composed of P2...Pn, and the outputs of the respective optical sensors are introduced in parallel to the detection circuit IO. However, in the previous embodiment, the two thin film transistors connected in series were used as the optical sensor, but in this embodiment, the three thin film transistors connected in series were used as the optical sensor. There are also three types of control signal waves given as gate voltages to these thin film transistors, and these three types of control signals φ1, φ2 . A signal line for φ3 is provided. That is, the thin film transistor T1. located on the left side of each optical sensor. l, T2. l,...Tn,
The gates of the + gates are collectively connected to the signal line of the control signal φl, and when the control signal φl is H, all of these thin film transistors are turned on. In addition, thin film transistors T1.2 and T2 located in the center of each optical sensor
．． 2. The gates of H+H++Tn2 are collectively connected to the signal line of control signal φ2, and when control signal φ2 is H
When , all of these thin film transistors are in the on state. Furthermore, thin film transistors T1.3, T2.3, ......"rn located on the right side of each optical sensor
, i are collectively connected to the signal line of the control signal φ3, and when the signal φ3 is H, these thin film transistors are all turned on. The detection circuit IO is the same as in the previous embodiment, and the analog switches A, .

Sample signal 31 sent in a time-division manner with a pulse width T
, S2...Receives Sn and turns on.

Next, the operation of this embodiment will be explained. First, the control signal φ
1, φ2, φ3 and sample signals SH, 32,...
...Sn will be explained based on FIG. 6.

The control signals φ1, φ2, and φ3 are rectangular waves with a period of T and a pulse occupancy rate of 273, and their phases are sequentially T.
/3 behind. Therefore, the control signals φl, φ2,
φ3 is sequentially brought into the L state for a time width of T/3. These control signals φ1, φ2, φ3 and sample signals Sl,
Regarding the relationship with S2, . . . , Sn, the period T of each control signal is the pulse width of the sample signal. Further, the sample signals Sl, 32, . Therefore, if we consider the case where the sample signal S+ is sent to the analog switch A1 and this analog switch AI is turned on, the light is The left thin film transistor T1. in the sensor P1. The control signal φ1, which is the gate voltage of l, is L
Therefore, only this thin film transistor T1.1 is turned off, and during the next T/3, the control signal φ2, which is the gate voltage of the central thin film transistor T1.2, becomes L, so only this thin film transistor T1.2 is turned off. It is in the off state, and during the last T/3, the right %1 film transistor T1
．． Since the control signal φ3, which is the gate voltage of 3, becomes L,
Only this fAN film transistor T1.3 is turned off. That is, while the analog switch AI is in the on state T, the thin film transistors T1. I, T1.2, T
1.3 becomes a photodetection element in units of T/3, and the photodetection signal at each position is sent to the amplifier 8 as a 3-bit serial signal. Below are analog switches A2, A3...
...An sample signals S2, S3...
Similar operations are performed sequentially when Sn is sent. That is, the photodetection signals at the positions of the Sn thin film transistors are sequentially transmitted to the amplifier 8 as a 3n-bit serial signal.
sent to.

As described above, in this embodiment, in a line sensor formed by arranging n optical sensors connected in parallel, the optical sensor becomes conductive when a gate voltage is applied and when the channel section receives light. ? , H1!2) consists of three transistors connected in series, and in each optical sensor, the plurality of 111il! ! 2) One of the thin film transistors was made to function as a photodetector without applying gate voltage for a certain period of time, and during that time, gate voltage was applied to the other thin film transistors to maintain conduction. Therefore, the number of elements on the board constituting the line sensor can be halved compared to the conventional example (shown in Figure 7), and the number of output signal lead wires provided for each optical sensor can be reduced compared to the previous example. It has the advantage of being able to use even fewer line sensors.

In turn, it becomes possible to significantly facilitate the manufacture of image sensors.

Note that this invention is not limited to the above two embodiments.

Various modifications can be made without departing from the scope of the invention.

[Effect of the invention 1] As explained above, this invention becomes conductive when a gate voltage is applied and when the channel part receives light (that is, it has both a switching function and a photodetection function) A light sensor is constructed by connecting a plurality of thin film transistors in series, and the application of gate voltage to one of the thin film transistors is stopped in sequence for a certain period of time to function as a photodetecting element. Since the gate voltage is continuously applied to the thin film transistor to maintain the conductive state, it is possible to suppress the increase in the number of lead wires that lead the output from the board on which the line sensor is formed to the external circuit as much as possible. This has the effect that the number of formed elements can be reduced, and the manufacturing of line sensors and, by extension, image sensors can be greatly facilitated.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the optical sensor and other circuits in an embodiment of the present invention, FIG. 2 is a diagram showing the structure of the optical sensor in FIG. 1, and FIG. 3 is a diagram showing the structure of the optical sensor in FIG. A circuit diagram of one embodiment, FIG. 4 is a time chart of each signal wave shown in FIG. 3, and FIG. 5 is a circuit diagram of another embodiment of the present invention, FIG.
The figure shows the time chart of each signal wave in Figure 5, and the time chart of each signal wave in Figure 7.
The figure is a circuit diagram of a conventional image sensor. l・,・Substrate, 2・φ, line sensor, 4. ...DC power supply, 10...detection circuit, P,,P2,...Pn
... Optical sensor, T1. I, T1.2,...T
n3...Thin film transistor. Patent applicant Casio Computer Co., Ltd. Figure 3 Lead Sn□-111 "1-1"

Claims (1)

[Claims] In an image sensor formed by arranging a plurality of optical sensors, the optical sensor is formed by connecting in series a plurality of thin film transistors that become conductive when a gate voltage is applied and when a channel part receives light. An image sensor characterized in that any one of the thin film transistors sequentially functions as a photodetecting element.