JPS63181370A - Document reader - Google Patents

Abstract

PURPOSE:To unnecessitate the IC chip mounting process to be performed when an analog switch is used by a method wherein a switching element is formed using the thin film transistor made of the material such as a-Si:H in the same manner as the thin film transistor to be used for selection of a sensor and group selection. CONSTITUTION:In the document reader in which the switching element 34 directly connected to a driving circuit 37 and the switching element 35 connected to the driving circuit 37 through an inverter 38 are connected through the intermediary of a group selection thin film transistor 29 against the sensor 22 which is divided into groups, a switching element is formed by the thin film transistor made of a-Si:H formed on the same surface of the substrate together with the sensor 22 and the group selection thin film transistor 29. As a result, the process of IC mounting is unnecessitated as in the case of an analog switch, and the manufacturing process of the title reader can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a document reading device using a contact type photoelectric conversion device that does not use a lens, such as in a facsimile machine or the like.

2. Description of the Related Art Conventionally, as a contact-type document reading device used in this type of facsimile, etc., a device as shown in FIG. 4 has been proposed in Japanese Patent Laid-Open No. 80-97765. This is made up of a plurality of MOS transistors 3 whose gates are connected to a shift register 2 via a control line 1, and whose sources are connected to a signal line 4.5 every other time. Here, the light receiving element (sensor) 6 is shown as a parallel circuit of a capacitor and a diode. The output signals generated on the two signal lines 4.5 are amplified by amplifiers 7 and 8, respectively, and then one is sent to the child terminal of the differential amplifier 12 via a changeover switch 9 and two sample and hold circuits 10 and 11. The other one is input to one terminal of the differential amplifier 12 via the changeover switch 13. Further, the output of the differential amplifier 12 is connected to an output terminal 15 via a switch 14. Here, the changeover switches 9 and 13 and the switch 14 are controlled by input signals to the terminals 16 and 17, and are turned on when the gates of the MOS transistors constituting these switches are at H level. Also, the two sample and hold circuits 10.11 are controlled by input signals to terminals 18.19, and these input signals are
When the input signal is at the L level, the input signal is in the sample state, and when the input signal is at the L level, it is in the hold state.

Here, a part of the sensor is formed by depositing a-Si:H by decomposing the source gas S L H using a plasma CVD method, and forming this as a photoelectric conversion film. This photoelectric conversion method is an accumulation type. A signal from a part of the sensor is output depending on whether the MoS transistor is turned on or off. Here, the readout part has already been integrated into an IC. In addition, as shown in FIG. 4, improving the S/N ratio by eliminating noise components through differential amplification of the signal between a part of the sensor and the dummy sensor is achieved by using two signal lines 4 as shown in FIG. , 5 are provided, and the noise caused by the MOS transistor 3 is canceled out by the same MOS transistor 3. In the illustrated example, the output of the MOS transistor 3 which switches and reads the signal of the light receiving element 6 is distributed to a plurality of signal lines 4 and 5, and the M
After the OS transistor 3 is continuously switched twice and the outputs obtained on the signal lines 4 and 5 are separated into a plurality of signals by the changeover switches 9 and 13 controlled by the MOS transistors, the plurality of signals are transferred to a differential amplifier. 12 to differentially amplify the image signal.

The problem that the invention aims to solve is that in the conventional sensor, an analog switch called a Mo3) transistor is used in the block drive part and readout part of the sensor, and the mounting process using an IC chip is required. is necessary. This increases costs and makes the manufacturing process complicated.

Means for Solving the Problems A switching element directly connected to a drive circuit and a switching element connected to the drive circuit via an inverter are connected to grouped sensors via group selection thin film transistors. In the document reading device, the switching element is formed by a thin film transistor made of a-8i:H, which is formed on the same surface of the substrate as the sensor and the group selection thin film transistor.

The switching element part that performs block drive on the action sensor and reads out the signal is formed by a thin film transistor made of a-3i:H, similar to the sensor and group selection thin film transistor, so it can be used as an analog switch. This eliminates the need for an IC chip mounting process and simplifies the manufacturing process.

Embodiment An embodiment of the present invention will be described with reference to FIGS. 1 to 3. First, a sensor array 21 is formed on an insulating transparent substrate 20 such as glass. This sensor array 21 is made up of a large number of sensors 22 arranged in a row at equal pitches.

This sensor 22 is a planar type sensor that utilizes the photoelectric effect of a-3i:H formed by plasma CVD. Specifically, as shown in FIG. 1, a transparent insulating film 23 made of Sin is formed on a substrate 20, and a 1-a-3i:H film 24 and an n''-a film are formed thereon as a photoelectric conversion film. -3i:H film 25 is formed in order, and n''-a-3i:H film 25 is formed on the 1-a-3i:H film 24.
The common electrode 26 and the individual electrodes 27 are formed as an ohmic contact layer so as to face each other in a plane. These electrodes 26,27 are by vapor deposition of MO.

There are two types of incident methods for the reflected light from the document surface to the sensor 22: sensor-side front-side incidence and substrate-side back-side incidence; here, the substrate-side back-side incidence method, which can obtain twice the photocurrent, is adopted. There is.

Further, these sensors 22 are grouped into one block. The common electrode 26 side is connected to a bias power supply 28. On the other hand, each sensor 22
A group selection thin film transistor (TPT) 29 is connected to the individual electrode 27 side of each.

Furthermore, a dummy sensor 30 having the same electrical characteristics as the sensor 22 is formed on the substrate 20 and is located near the sensor at one end of the sensor array 21 in the array direction.

That is, this dummy sensor 30 is also of the Brenna type,
510. on the substrate 20. 1-a-8i:H film 24 and n''-a-Si:
A H film 25 is sequentially formed, and a common electrode 26 and an individual electrode 27 are formed thereon in a planarly opposed state by MO evaporation. However, this dummy sensor 30
A light-shielding film 31 made of Cr is formed on the lowermost layer of the substrate 20 so that no light is always incident on the substrate 20 .

The common electrode 26 of this dummy sensor 30 is also connected to the bias power supply 28.

Next, a bias power supply 32 is connected to the gate of the group selection thin film transistor 29, and a TPT driving IC 33 for controlling on/off is connected to the gate of the group selection thin film transistor 29 in each block. are set to drive at the same time.

Further, for the sensors 22, thin film transistors 34 and 35 serving as signal reading switching elements are provided in a number twice as many as the number of sensors 22 in each block.

These thin film transistors 34 and 35 are all connected to the group selection thin film transistor 29 via a matrix wiring circuit 36. Here, such two thin film transistors 34 and 35 are paired as one.
It acts on the output for bits, and the gate on the thin film transistor 34 side is directly connected to the drive circuit 37, and the inverter 38 is interposed to the gate on the thin film transistor 35 side. As a result, in a pair of thin film transistors 34 and 35, when one thin film transistor 34 or 35 is on, the other thin film transistor 35 or 34 is off, and the ground level is always determined, so that no loop current from other bits occurs. It is set. Here, the drive circuit 37 and the inverter 38 are configured as a TPT drive IC 39. That is, the TPT driving IC 39 applies reverse positive and negative (on and off) bias signals to each pair of thin film transistors 34 and 35 at the same timing.

The output from the thin film transistor 34 is input to an operational amplifier 40. Correspondingly, the dummy sensor 30 is also connected to an operational amplifier 41. The outputs from these operational amplifiers 40 and 41 are input to a differential amplifier 42, and the differential output signal is obtained from an output terminal 43.

Here, these thin film transistors 29, 34.degree. 35 all have the same structure, and the structure is shown in FIG. First, a gate electrode 4 is formed on a substrate 20 by Cr sputtering.
4 and on top of this, 5i as in the case of sensor 22.
A transparent insulating film 23 made of nR is formed, and 1-a is formed on it.
- A state in which a Si:H film 24 and an n''-a-5i:H film 25 are formed in this order, and a source electrode 45 and a drain electrode 46 are opposed in a plane by Mo/AQ evaporation thereon. It is formed by

Therefore, considering the overall structure, first, a Cr film is formed on the substrate 20 by sputtering, and a predetermined pattern is formed by chemical etching or the like to form the light shielding film 31 and the gate electrode 44. Here, the dummy sensor 3
Unlike the storage type, light enters from the substrate 20 side, so a light shielding film 31 is required to shield this light. However, the light shielding film 31 of such a dummy sensor 30
When forming the gate electrodes 44 of the thin film transistors 29, 34, and 35 described above, the Cr film is also used as a dummy sensor 3.
They are formed simultaneously by forming a pattern at the 0 formation position. In other words, it can be easily formed without adding a process dedicated to the light shielding film of the dummy sensor 30. Also, considering these thin film transistors 29, 34, 35, unlike the sensor 22, it is better to prevent light from entering the thin film transistors. It is something that can be given a function.

In this respect as well, a process for forming a light-shielding film exclusively for the thin film transistors 29, 34, and 35 is not necessary, and manufacturing can be simplified.

After forming the light shielding film 31 and the gate electrode 44, an insulating film 23.1 made of SiO is formed by plasma CVD.
-a-St:H film 24, n''-a-3t:H film 25 are sequentially laminated-0 By this, not only the sensor 22 but also the
Even in thin film transistors 29, 34°35, a-Si
:H material is used for the semiconductor layer. After this, sensor electrodes 25.26 and source/drain electrodes 45.46 are formed by vapor deposition of Mo or Mo/AQ. Patterning of these electrodes is done by chemical etching. Further, patterning of the n''-a-Si:H film 25 in the sensor 22 or the thin film transistors 29, 34, 35, and further in the dummy sensor 30 is performed by removing unnecessary portions by dry etching. The example sensor 22 is based on an active matrix drive system,
Matrix wiring processing is also performed between the thin film transistor 29 and the thin film transistors 34 and 35 when forming their electrodes. In the matrix circuit 36 portion, a polyimide film is formed as an interlayer insulating film, and the upper and lower electrodes are electrically connected by through holes. Such a matrix circuit 3
AQ may be used as the wiring metal material for the 6 portions, and patterned by chemical etching. Further, the TPT driving IC 33 is mounted on the substrate 20 and connected by wire bonding.

By the way, the read optical signals from each sensor 22 are sequentially taken into the operational amplifier 40 through the switching operations of the thin film transistors 29, 34, and 35 mentioned above, and the current -
It is extracted as a voltage-converted signal. The signal from the sensor 22 has a waveform as shown in FIG. 3(a), for example. As shown in this waveform, the sensor signal may be affected by, for example, noise components of the sensor itself, spike noise, and the like. However, since the photocurrent signal from the dummy sensor 30 is current-voltage converted by the operational amplifier 41 and input to the differential amplifier 42, where it is differentially calculated with the signal from the sensor 22 side, such noise components are canceled out. It will be removed. That is, the dummy sensor 30 is in a state where no light enters due to the light shielding film 31, has the same structure and the same electrical characteristics as the original sensor 22 except for the light shielding film 31, and is located very close to one end of such sensor 22. Therefore, the dummy signal obtained from the dummy sensor 30 is the dark current component plus the noise component of the sensor itself, as shown in FIG. 3(b). Therefore, by differentially amplifying this dummy signal and the sensor signal, a differential output from which noise components have been removed can be obtained from the output terminal 43, as shown in FIG. 3(C).

Therefore, the sensor output can be read with a good S/N ratio.

Effects of the Invention In the present invention, as described above, the switching element for reading the sensor output is formed by a thin film transistor formed on a substrate using the a-3i:H material, similar to the sensor and group selection thin film transistor. This eliminates the need for the process of mounting an IC chip as in the case of 2009, which simplifies the manufacturing process and reduces costs.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention,
FIG. 1 is a sectional view showing different cross sections together, FIG. 2 is a circuit diagram, FIG. 3 is a signal waveform diagram, and FIG. 4 is a circuit diagram showing a conventional example. 20... Base plate, 22... Sensor, 29... Group selection thin film transistor, 34.35... Thin film transistor (switching element), 37... Drive circuit,
38...Inverter

Claims (1)

[Claims] A document reading device in which a switching element directly connected to a drive circuit and a switching element connected to the drive circuit via an inverter are connected to grouped sensors via group selection thin film transistors, A document reading device characterized in that the switching element is formed by a thin film transistor made of a-Si:H, which is formed on the same surface of a substrate as the group selection thin film transistor.