JPH01239883A - Piezoelectric converting element - Google Patents

Abstract

PURPOSE:To arrange the structure that the dependency gamma of output current to the quantity of incident light may be larger than 1 by performing light irradiation under the condition where a gate voltage is applied to a gate electrode and by using a photodiode of a thin film as the gate electrode as a photoelectric converting element which generates an output current between source drain electrodes. CONSTITUTION:In a photoelectric converting element which generates an output current between source drain electrodes 2s and 2d by performing light irradiation under condition where a gate voltage is applied to a gate electrode, a photodiode 61 of a thin film is used as a gate electrode. For example, an a-Si:H film which is formed by a P-CVD method is used as a semiconductor layer 3, and a photoelectrode 61 at a gate electrode part is made into a pin-type element of a thin film, and S2O2 or ITO film 7 is provided on the light irradiation side to form an electrode. And the photodiode 61 is made thin as far as possible so that the light may enter easily up to a semiconductor layer 3. Also, in the case of reverse stagger type structure as shown in Figure (a), the light is irradiated from the side of a glass substrate 1, and in the case of a top gate stagger type as shown in Figure (b), the light is irradiated from the top.

Description

[Detailed Description of the Invention] [Required 1] Regarding a photoelectric conversion element that converts incident light into an electrical signal, in a transistor-type photoelectric conversion element, the dependence γ of the output current on the amount of incident light is greater than 1. With the aim of achieving .

[Industrial application field]

The present invention relates to a photoelectric conversion element that converts incident light into an electrical signal.

[Prior Art] When sensing light and converting it into a signal, a method of converting light into electricity using a semiconductor is generally used.

There are roughly four types of means for converting light into electricity using semiconductors:

■Photoconductor detectors that utilize the photoconductive effect, such as a-5i, CdS, and PdS.

■ Junction diode type detector using various junction diodes such as 5chottky, pn, pin, etc.

■Transistor-type detectors that use junction transistors, field-effect transistors, etc.

■An electronic avalanche photodiode that uses an electronic avalanche mechanism.

FIG. 6 is a cross-sectional view of a conventional transistor-type detector (2), showing an MZS-type transistor structure. 1A shows a top gate staggered type, in which a source electrode 2s, a drain electrode 2d, a semiconductor layer 3, a gate insulating film 4, and a gate electrode 5 are stacked in this order on an insulating substrate 1. When used as a phototransistor, light is made to enter from the gate electrode 5 side.

(b) is an inverted staggered type, in which a gate electrode 5, a gate insulating film 4, a semiconductor layer 3, a source electrode 2S, and a drain electrode 2d are laminated in this order on an insulating substrate 1.

When used as a phototransistor, light is made to enter between the source electrode 2s and the drain electrode 2d.

Furthermore, in a thin film transistor in which the insulating substrate 1 is made of a light-transmissive material such as glass, light can be irradiated even from the insulating substrate 1 side.

[Problems to be Solved by the Invention] In the case of the photoconductor detector (2), although the gain is the largest among the four types, it has the disadvantage of slow response speed.

The junction diode type detector (2) has the fastest response speed, but has a small gain of 1 or less.

The transistor type detector (2) has a gain inferior to the photoconductor detector (2), but is larger than the junction diode type detector (2), and its response is inferior to the junction diode type detector.

The electron avalanche photodiode (2) has a response close to that of the junction diode detector (2) and a gain close to that of the photoconductor detector (2), but the device configuration is difficult.

In addition, in any structure from ■ to ■, the output (current Iph)
(7) Incident light fNph dependence Iph cr(Nph)
'If you look at it, T≦1. As a result, it is impossible to make the S/N ratio of the output with respect to the incident light higher than the ratio of the amount of incident light. Moreover, conventionally, when the absolute value of the output photocurrent is increased, the dependence on the amount of incident light decreases, and the output photocurrent ratio decreases.

The technical problem of the present invention is to solve this problem in the transistor type detector (2) and to improve γ so that T≧1.

[Means to solve the problem]

FIG. 1 is a sectional view illustrating the basic principle of the photoelectric conversion element according to the present invention, in which (a) is a top gate staggered type;
(b) is an inverted stagger type. (a) In (b),
6 is a photodiode, and the photodiode 6 is provided as a gate electrode in a transistor type detector.

2 is an insulating substrate, 2s is a source electrode, 2d is a drain electrode, 3 is a semiconductor layer, and 4 is a gate insulating film.

[Effect]

By using the photodiode 6 as the gate electrode, the gate potential changes depending on the amount of incident light, and the operating point changes.

A conventional transistor as shown in FIG.
In the case of h)→current (Iph) conversion, there is a large gain of 102 or more, but the light intensity dependence of source/drain current: γ
is less than 1, and its dependence: ■2. α(Nph) is
Depends on gate voltage.

That is, V9-1. shown in FIG. 2(a). . As a characteristic, as the gate voltage increases, the value of the output current flowing between the source and drain increases. Furthermore, if the intensity of the light irradiated to the photoelectric conversion element is weak like Ll, the output current will only have the value ILL as shown by the broken line, but the light intensity will be Ll.
If it is as large as IO, a large output current can be obtained, as shown by the solid line. In other words, the number of incident photons is N. The currents generated with the number of incident photons N p h 1 (Ni, .=1ONph+) are I L11+ and ILI, respectively.

Therefore, at a certain gate voltage Vgl, the difference in output current value depending on the intensity of the irradiation light amount is iLl.

It becomes 10.

Generally, when an n-type semiconductor layer is used, T is smaller than 1 in the accumulation region (gate voltage, positive), and γ=1 in the depletion inversion region (gate voltage, negative). Therefore, in a region where the gate voltage is negative, in the case of a signal where the amount of incident light is 10:l, in a region where the gate voltage is positive, this indicates that the rate of change in current relative to the rate of change in light amount is always less than 1. There is currently nothing that can increase this to 1 or more.

However, according to the present invention, by replacing the gate electrode with the photodiode 6, the gate potential changes depending on the amount of incident light, and the operating point changes, so that T≧1.

In other words, the photovoltaic force of the photodiode is e
l.

(+1.: photocurrent, 1.: saturation current in dark)
It is expressed as , and changes as LIL with respect to a change in It. Here ■. C corresponds to the gate voltage, and depending on the difference in the amount of incident light, V91-VOCI "ikT/e ・Q n (IL
I/ +5) Vq+o = Voc+o=kT/ e-
1n (IL+o/Is), which means that it was observed with a different gate voltage.

FIG. 2(b) illustrates this pattern. When the amount of irradiation light shown on the horizontal axis increases from L1 to L1°, the photovoltaic force (■) corresponds to the gate voltage. I will increase.

As a result, according to the present invention, the amount of irradiated light changes from Ll to Ll.

, the photodiode 6 causes the gate voltage to increase to ■9. As a result, as shown in (a), the output current value increases from the black circle (1) on the broken characteristic line to the value of the black circle (2) on the solid line, and the output current value increases from The difference is ILI・. This is larger than the conventional value iL1·1°, and γ≧1.

More specifically, when the conventional gate electrode is a transparent electrode, metal, etc., Nphl. /N□1, the signal ratio is uniformly determined for a given ■9, and the signal is increased (■
9 positive), the signal ratio will become smaller, and if the signal ratio is increased (
(2) When the signal is negative (9), the absolute value of the signal decreases. On the other hand, in the present invention, as is clear from the difference between black circles (1) and (2) in the figure, the signal ratio is large and the absolute value is also large.

[Example] Next, how the photoelectric conversion element according to the present invention is actually implemented will be explained using an example. In FIG. 3(a), P-
The a-5i;It film formed by the CVD method is used as the semiconductor layer 3.
The case where it is used as The photodiode 61 in the gate electrode section is a thin film pin type element, with 5iOz on the light irradiation side.
An ITO film 7 is provided as an electrode. These are formed as thin as possible so that light can easily enter the semiconductor N3. In other words, the thickness is set to such an extent that the light to be used reaches the channel portion after being transmitted.

(a) shows the device actually used, and (b) shows an example of its application. In case (a), the ISO current under white light is 25 f
Approximately 2XIO-7A/1 element (one element has an opening of approximately 40 μm), 2. Approximately 1.5X10-8 under iX
A/1 element was obtained. FIG. 4 shows the measurement results when the gate electrode portion is made of only SnO□. 25I! , under X irradiation, to reduce 130 to 2 Xl0-7A/1 element, ■.

must be approximately IV, in which case at 2.542X it becomes 5
X/2.5I! , X = 10, the output signal ratio 2
X10-'15X10-'=4, and 2 xlO-7/ when using a photodiode as the gate electrode.
It is inferior to 1.5xlO-'=13.

In the case of the inverted staggered structure in (a), light is irradiated from the glass substrate 1 side, but in the case of a top gate staggered structure as shown in (b), it is possible to irradiate from the top. Also(
In a structure like b), it is also possible to use a C-5i substrate as the semiconductor layer and form the photodiode 61 with an a-5ill or C-3i film by P-CVD or 301 technology.

Further, by providing multiple stages of diodes 61 in the gate portion, the output current value can be further increased. FIG. 6 shows a multi-stage structure in which photodiodes 61 .

Note that in the present invention, in addition to using a photodiode as a gate electrode, a conventional gate electrode and a photodiode can be stacked.

〔Effect of the invention〕

As described above, according to the present invention, a photodiode is provided as a gate electrode in a transistor type detector, and the photoelectromotive force of the photodiode changes as the amount of light changes, thereby changing the gate voltage. Therefore, in the photoelectric conversion element of the present invention, the source/drain current changes due to changes in both the irradiation light amount and the gate voltage, the dependence γ of the output current on the incident light amount becomes Ta2, and the absolute value of the output photocurrent also changes. To increase. In this way, the output ratio of the output current signal increases, and the output S
/N ratio can be made greater than the incident light amount ratio.

[Brief explanation of the drawing]

FIG. 1 is a sectional view explaining the basic principle of the photoelectric conversion element according to the present invention, FIG. 2 is a characteristic diagram explaining the details of the present invention, FIG. 5 is a cross-sectional view showing another example, and FIG. 6 is a cross-sectional view showing a conventional photoelectric conversion element. In the figure, ■ indicates an insulating substrate, 2S indicates a source electrode, 2d indicates a drain electrode, 3 indicates a semiconductor layer, 4 indicates a gate insulating film, 5 indicates a gate electrode, and 6.61 indicates a photodiode. Patent applicant Fujitsu Co., Ltd. sub-agent Patent attorney Yasushi Fukushima Yasushi Bunda (Italian Figure 3 - Kui (CL) I'll use the Ying Ming Figure 2 (b) Wood Yang - T. After Nreli Ding. Figure 5

Claims (1)

[Claims] 1. In a photoelectric conversion element that generates an output current between source and drain electrodes (2s) (2d) by irradiating light with a gate voltage applied to the gate electrode, a thin film is used as the gate electrode. A photoelectric conversion element characterized by using a photodiode (6). 2. The photoelectric conversion element according to claim 1, wherein the thin film photodiode is made of an a-Si;H film formed using P-CVD, photo-CVD, or the like. 3. The photoelectric conversion element according to claim 1, characterized in that the thin film photodiode is provided in two or more layers.