JPS594183A - Color detecting system - Google Patents

Abstract

PURPOSE:To enable to discriminate multiple colors with a sole element on the basis of the displacement of a peak point of a current value at each applied voltage by varying the value of reverse bias applied to a photodiode at two stages and more. CONSTITUTION:When a reverse bias is applied to a diode 7, a depletion layer is generated in a Schottky junction between an i-type layer 3 and a platinum layer 4, and a current flowed in a photocarrier, but when the value of a reverse bias is increased, the extension of the depletion layer gradually increases. However, when the wavelength of the incident light is short, the light of the short wavelength can be relatively effectively absorbed when the extension of the depletion layer is small. When the reverse bias is increased to extend the depletion layer, the light gradually decreased the relative sensitivity, but when the wavelength of the light is long, the sensitivity gradually increases, it reaches the peak point at the long wavelength side as compared with the voltage V1. As a result, when the reverse bias is increased from the voltage V1 to the voltages V2, V3, the peak point of the sensitivity is gradually displaced to the long wavelength side. Accordingly, the value of the reverse bias is switched by a measuring circuit, the current value for each bias voltage is detected across a detecting resistor 8, and the output ratio is measured. In this manner, the color can be discriminated from the output ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Technical Field of the Invention The present invention relates to a color detection method suitable for color detection in a facsimile reader section or the like.

fbl Prior Art and Its Problems FIG. 1 is a diagram schematically showing a conventional semiconductor color sensor, which has a structure in which an N layer is sandwiched between a P layer below the . Then, terminals are drawn out from the P layers on both sides and the NN in the center to form a three-terminal configuration, and a current value of 11, 2 during light reception is detected between the common terminal in the center and the terminals of the P layers on both sides. It determines the frequency of light emitted and identifies colors.

That is, the frequency of light can be detected by measuring the ratio of the current value 12 between the lower P layer and the N layer to the current value It between the upper P layer and the N layer. .

Furthermore, in the conventional single-crystal color sensor, it is necessary to provide a terminal between the diodes connected in opposite directions, which complicates the structure. In addition, if it is made of amorphous Si, in order to take out the intermediate electrode,
The diode manufacturing process must be divided into two steps, which significantly reduces manufacturing efficiency. Alternatively, in order to take out the intermediate electrode, it is necessary to accurately detect the midpoint of the diode 1z, but the process becomes complicated, which causes difficulties in drawing out the terminal. Furthermore, in terms of performance, the response speed is slow; 1.
11 There are also problems such as low power.

On the other hand, there is a color sensor that uses amorphous Si and has a color filter function for each color, but since it is composed of a plurality of elements, the structure is complicated and it is difficult to miniaturize.

(C) Purpose of the Invention The present invention solves these problems in the conventional color detection method and simplifies the manufacturing process such as terminal extraction by making it possible to perform color detection even in a two-terminal structure. The present invention also aims to improve detection performance and to enable multi-color discrimination with a single element, unlike a multiple element configuration in which each color has a color filter function.

Structure of fd+ Invention In order to achieve this object, the present invention is a method of detecting the color of light by applying a reverse bias to one photodiode, and the value of the applied reverse bias voltage is set in two or more levels. The color of the received light is determined based on the shift of the sensitivity peak point at each applied voltage.

[81 Embodiments of the Invention Next, examples will explain how the color detection method according to the present invention is actually implemented. Figure 2 is a cross-sectional view of a two-terminal color sensor, for example, on a substrate such as glass.
Molybdenum N1 is deposited, and then an n layer 2 made of amorphous Si doped with about 500 deformed phosphorus (P) is formed, and the amorphous layer 2 is formed on -1- of the layer 2 by a glow discharge method or the like. i IN 3 made of fas Si is 1
It is formed to a thickness of approximately μm. And amorphous Si doped with poron (B) on this i If 3
The P layer 4 consisting of P 2 is formed by about 500 layers, and finally the electrode 5 is formed of indium oxide (Ir+z Oy) or the like to take out the terminal.

In order to detect color with this diode I, a bias power supply 6 is connected between the electrode 5 and the molybdenum electrode 1, and a reverse bias is applied.In the present invention, the value of the bias voltage at this time is changed stepwise. , and detect the peak point of sensitivity for each bias voltage.

FIG. 3 is a diagram showing a detection circuit in which the bias voltage can be switched in this manner. A bias power source 61. 62 and 63 can be selectively connected. That is, one terminal of the bias power supplies 6162 and 63, each having a different terminal value, is connected in common, while the other terminal is selected by the changeover switch 9.

FIG. 4 shows sensitivity characteristics depending on wavelength, where the horizontal axis represents wavelength and the vertical axis represents relative sensitivity. Curve 1 shows the sensitivity when bias power supply 61 is applied.
is the sensitivity when bias power supply 62 is applied, curve ■3
1 and 2 respectively indicate the sensitivity when the bias power supply 63 is applied. That is, when a reverse bias voltage is applied to the diode 7 configured as shown in FIG. As the value increases, the depletion layer gradually expands. However, when the wavelength of the incident light is short, the smaller the spread of the depletion layer, the more effectively the short wavelength light is absorbed, and as a result, the fourth
It exhibits characteristics as shown in curve 1 in the figure. As the reverse bias is increased and the depletion layer is expanded, the relative sensitivity of the light described above gradually decreases, but for light with a longer wavelength, the sensitivity gradually increases. The peak point is reached on the longer wavelength side than at Vl.

As a result, as the reverse bias is increased from Vl to V2 and V3, the peak point of sensitivity gradually shifts toward longer wavelengths.

Therefore, by switching the reverse bias value using the measurement circuit shown in Figure 3, detecting the current value for each bias voltage at both ends of the detection resistor 8, and measuring the output ratio, the color can be determined from the output ratio. can be determined. If there are only two bias voltages, the output ratio may be the same, but
Measure three or more bias voltages, Vl, V2, and V3,
For example, when the output is expressed as f (V), f (Vi
) / f (Vi) to f (Vi) / f
(V3), the wavelength can be detected regardless of the amount of light. In other words, by detecting the respective ratios of the sensitivity for the bias voltage V+, the sensitivity for the bias voltage ■2, and the sensitivity for the bias voltage v3 for the wavelength λ1, the wavelength corresponding to the incident light can be determined. 6- Can be distinguished.

(f1 Effect of the invention y As described below-1-, according to the present invention, the color of light is detected by applying a reverse bias to one photodiode, and the value of the applied reverse bias is set to 2. The color of the received light is determined based on the deviation of the peak point of the current value for each applied voltage.As a result, the diode used is 1 f
llil, so there are only two lead-out terminals, and even when the terminal is drawn out in a cylinder and the diode is constructed from amorphous Si, etc., it can be made in a simple process and can be made from a single element. Since the sensor can be configured with a small number of lead-out terminals, the sensor can be made smaller and can be arranged in a high-density arrangement. In addition, the bias voltage applied between the two terminals is changed in two or more stages, and the wavelength of the received light is detected based on the shift in the peak sensitivity value at each bias voltage. In addition to being possible,
Since a bias voltage is applied, the output is large and the response speed is fast.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing a color sensor according to the present invention, FIG. 2 is a sectional view showing a color sensor according to the present invention, FIG. 3 is a diagram showing a circuit configuration for wavelength detection, and FIG. It is a diagram showing the characteristics of wavelength and coherence. In the diagram, 1 and 5 are electrodes, and 3 is amorphous 5it.
e, 6 is a bias power supply, 61, 62, 63 are bias power supplies, 7 is a photodiode, and 8 is a detection resistor, respectively. Patent Applicant: Fujitsu Limited Agent, Patent Attorney: Minoru Aoyagi - Natsashi μ Kano ~

Claims (1)

[Claims] This method detects the color of light by applying a reverse bias to one photodiode, and the value of the applied reverse bias voltage is varied in two or more steps, and the shift in the peak point of sensitivity at each applied voltage is A color detection method that distinguishes the color of received light based on the color of the received light.