JP3005806B2 - Photodetector - Google Patents

Description

Description: Object of the Invention (Industrial application field) The present invention relates to a photodetector, and more particularly to a photodetector capable of changing wavelength characteristics and a color sensor using the same. .

(Prior Art) There are two types of banknote identification, identification by light and identification by magnetism.

Of these, the red light photodiode (PD), which detects red light, the green photodiode, which detects green light, and the blue photodiode, which detects blue light, are conventionally arrayed. Are measured and superimposed, and this is used as a detection result.

That is, the light intensity is measured and superimposed by using diodes having sensitivity peaks for each of two colors such as red and green, and green and blue, and the colors are identified. For this reason, there is a problem that accurate color identification cannot always be performed. If the light intensity is measured and superimposed using diodes having sensitivity peaks for the three colors of red, green and green, the color can be distinguished well.
There is a problem that the area occupied by the sensor increases and resolution cannot be sufficiently obtained.

By the way, in actual reading, conventionally, for example, a method of sequentially arranging diodes of each color in a line or arranging a diode array of each color is adopted.

As described above, since a large number of diodes must be formed within a limited area, there is a problem that it is extremely difficult to increase the resolution.

(Problems to be Solved by the Invention) As described above, in the conventional photodetector, a large number of diodes must be formed in a limited area.
There is a problem that it is extremely difficult to increase the resolution while performing high-precision color identification.

This is not limited to the banknote recognition device, but has the same problem with other detection devices including an optical sensor for color identification.

The present invention has been made in view of the above circumstances, and has as its object to provide a photodetector capable of highly accurate color identification.

Another object of the present invention is to provide a high-precision photodetector with high resolution.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, an invention according to claim 1 includes a semiconductor substrate of a first conductivity type, and a plurality of semiconductor substrates arranged in an array at a predetermined interval on a surface of the semiconductor substrate. A second conductive type semiconductor region, a plurality of second electrodes formed so as to contact the respective semiconductor regions, and a region corresponding to the periphery of the respective semiconductor regions, formed on the substrate. A second electrode; a third electrode configured to contact the substrate; and a voltage supply device for applying a predetermined voltage between the first electrode and each of the second electrodes. A photodetector configured to measure a current between the first electrode and the third electrode, wherein a voltage applied to each of the first electrodes is different for each of the semiconductor regions. The semiconductor substrate and the semiconductor region Pn formed between
By controlling the extension of a depletion layer formed at the junction, light detection in a desired wavelength region is performed for each of the semiconductor regions, and multicolor reading is enabled.

Further, the invention according to claim 2 is a semiconductor substrate of the first conductivity type, a plurality of semiconductor regions of the second conductivity type arranged in an array on the surface of the semiconductor substrate at predetermined intervals. A plurality of first electrodes formed to contact each semiconductor region, a second electrode formed on a part of the substrate at a position corresponding to the periphery of each semiconductor region, and a contact with the substrate And a voltage supply device for applying a predetermined voltage between the first electrode and each of the second electrodes. The first electrode and the third electrode In the photodetector configured to measure the current between, the applied voltage to each of the second electrode is variable in a plurality of stages,
The same region is read with a plurality of different applied voltages, and pn formed between the semiconductor substrate and the semiconductor region
By controlling the extension of the depletion layer formed at the junction,
Light is detected in a desired wavelength region each time, and multicolor reading is enabled.

(Operation) According to the first configuration, the potential is formed between the semiconductor substrate and the semiconductor region by changing the potential of the second electrode on the substrate with respect to the first electrode contacting the semiconductor region. By controlling the extension of the depletion layer formed in the pn junction, the wavelength characteristics are made variable, so that one element can perform light detection in different wavelength ranges and a certain range. It is also possible to perform optical detection in an analog manner over the entire wavelength range.

According to the second configuration, the same photodetector is formed in an array on the substrate, and only the applied voltage is controlled.
Since the sensitivity regions of these elements can be formed differently, high-precision multi-color reading can be performed with an extremely simple configuration.

Further, according to the third configuration, the same photodetector is formed in an array on the substrate, and reading is performed a plurality of times by changing the applied voltage to the same region.
Not only can the resolution be improved, but also highly accurate multicolor reading can be performed with a very simple configuration.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment 1 As a first embodiment of the present invention, a wavelength characteristic variable photodiode will be described.

As shown in FIGS. 1 (a) and 1 (b), the photodiode has a p ⁺ diffusion layer 2 formed on the surface of an n-type silicon substrate 1 and a silicon substrate 1 formed therearound. N ⁻ diffusion layer 3 having a lower concentration than indium tin oxide (IT) formed so as to contact p ⁺ diffusion layer 2
O) formed on the surface of the n ⁻ diffusion layer 3 via the first electrode 4 made of O) and the insulating film 5 made of a thin silicon oxide film.
And a third electrode 7 formed on the back surface of the substrate 1 for measuring a photocurrent flowing between the first electrode and the third electrode. By doing so, the light intensity is detected.

Here, the second electrode is configured so that the potential with respect to the first electrode can be changed from positive to negative. By changing the potential of the second electrode with respect to the first electrode, the silicon substrate 1 and the p ⁺ diffusion layer 2 can be changed. By controlling the extension of a depletion layer formed in a pn junction formed between the first and second layers, the wavelength characteristic is made variable.

That is, when the potential of the first electrode is set to the ground potential and the potential of the second electrode is set to a large positive potential, the depletion layer is formed as shown in FIG. Since the light that has arrived at this point is read, light having a relatively long wavelength can be detected.

When the second electrode is set to a negative potential, the depletion layer becomes the second potential.
As shown in FIG. 2B, the light is read out in a relatively shallow region in the silicon substrate because the light is read out in a relatively shallow region in the silicon substrate. it can.

Wavelength detection can be performed by comparing measured values in each of these modes by division processing or the like.

Alternatively, the detection may be performed by continuously changing the potential of the second electrode.

According to this photodiode, it is also possible to detect the light intensity of a desired wavelength by changing the applied voltage with one element.

In the embodiment, n ⁻ around the p ⁺ silicon layer 2.
The diffusion layer 3 was added to make it easier to form an aerial view layer.
The n ^- diffusion layer 3 is not necessarily required.

Embodiment 2 Next, a color sensor will be described as a second embodiment of the present invention.

This sensor has an equivalent circuit in FIG. 3, and FIGS.
As shown in the plan view and the cross-sectional view, the tunable photodiodes PD _{11 to} PD _n1 , PD _{12 to} PD _n2 , PD shown in the first embodiment.
_{13 to} PD _n3 ... Are arranged in an array, and different applied voltages are sequentially applied to every three rows, sensitivity is provided in three wavelength regions, and color reading is performed.

Ie, p-type silicon substrate 1, respectively in a region surrounded by the field insulating film 9 formed at predetermined intervals on the surface n ⁺ -type diffusion layer _{2 11 ~2 n1, 2 12 ~2} n2, 2 13 ~2 _n3 ... are arranged in an array, and these n ⁺ type diffusion layers 2 ₁₁ to 2 _n1 , 2 ₁₂ to 2 _n2 ,
2 _{13 to} 2 _n3 ... _Are formed, and the n ⁺ type diffusion layers 2 ₁₁ to 2
_A second electrode 6 made of tin oxide (SnO ₂ ) is formed so as to cover around _{n 1} , 2 _{12 to} 2 _n2 , 2 ₁₃ to 2 _n3 with a gate insulating film 5 interposed therebetween. The second electrode 6 is a common electrode, and a third electrode (not shown) is integrally formed on the back surface of the p-type silicon substrate. Further, the n ⁺ -type diffusion layer _{2 11 ~2 n1, 2 12 ~2} n2, 2 13 ~2 spaced from _n3 n ⁺ -type diffusion layer 2 _11S to 2 of electrode taken out _n1S, 2 _12S ~2 _n2S, 2 _{13S to} 2 _n3S
There is formed, the first electrode 4 _11-4 consisting of Al layer on the
_{n1, 4 12 ~4 n2, 4} 13 ~4 n3 ...... is formed.

The n ⁺ type diffusion layers 2 ₁₁ to 2 _{n 1} , 2 ₁₂ to 2 _{n 2} , 2 ₁₃ to 2 _{n 3} and the n ⁺ type diffusion layers 2 _11S to 2 n _1S and 2 _12S to 2 _{n 2S} and 2 _13S to 2 for electrode extraction
Between the _N3S, 2 two switches ing transistors TrV for switching the vertical and horizontal directions, TrH is disposed.

Each of the tunable photodiodes PD _{11 to} PD _n1 and PD ₁₂
... PD _n2 , PD _{13 to} PD _n3 ... Respectively transfer the gate voltages of the two switching transistors TrV and TrH to the vertical shift register SH V and the horizontal shift register SH H.
And the reading is performed sequentially.

V1, V2, V3 ... are vertical signal lines, and H1, H2, H3 ... are horizontal signal lines. Here, the vertical signal lines V1, V2, V3,... Are connected via contact holes h to a line V composed of a polycrystalline silicon layer arranged in parallel with a horizontal signal line composed of a polycrystalline silicon layer. . .. Between these horizontal signal lines H1, H2, H3.
An n ⁺ diffusion layer 8 is formed, and this is used as one of a source and a drain to form two switching transistors TrV and TrH.
Is configured.

When these switching transistors TrV and TrH are both turned on, the n ⁺ type diffusion layers 2 ₁₁ to 2 _{n 1} , 2 ₁₂ to 2 _{n 2} ,
2 _{13 to} 2 _n3 and n ⁺ type diffusion layer for electrode extraction 2 _11S to 2 _n1S , 2
_{12S to} 2 _n2S and 2 _{13S to} 2 _n3S are connected to the first electrodes 4 ₁₁ to 4
_{n1, 4 12 ~4 n2, 4} 13 ~4 n3 ...... from the signal read is to be carried out.

The extraction of the signal, as shown in the timing chart in FIG. 4, the first electrode _{4 11 ~4 n1, 4 12 ~4} n2, 4 13 ~4 n3
Have a first potential V1, a second potential V2, and a third potential V1, respectively.
The potential V3 is applied so that the red, blue, and green wavelength regions are sequentially detected in each column of the tunable photodiode array, and multicolor reading is performed. In addition, 10 is a channel stopper for preventing inversion,
Reference numeral 11 denotes an interlayer insulating film made of a PSG film.

The voltage applied to the second electrode 6 is changed three times so that the red, blue, and green wavelength regions can be sequentially detected at each time, and the color reading is performed by superimposing the three reading results. Reading can be performed.

As described above, in the color sensor according to the embodiment of the present invention, since the same element can detect light in different wavelength regions, the resolution can be tripled.

In the above embodiment, the same color is read for each bit, and this is repeated three times by changing the voltage. However, a different voltage may be applied to each column. Although this method does not theoretically increase the resolution,
Reading in a short time becomes possible. Further, since there is no need to provide a filter for each color, the structure may be simplified as compared with the conventional two-dimensional color sensor, and the resolution may be substantially increased in some cases.

In the above-described embodiment, the color sensor that performs two-dimensional reading has been described. However, the color sensor can be formed as a one-dimensional sensor array and used as a scanning type color reading device. In this case, after repeating reading two or three times while sequentially changing the applied voltage, the operation of scanning one bit at a time in the sub-scanning direction is repeated, so that high-precision reading can be performed with a simple device. .

〔The invention's effect〕

As described above, according to the present invention, a semiconductor region of another conductivity type is formed on the surface of a semiconductor substrate of one conductivity type.
By forming a pn junction and changing the potential of a second electrode contacting the semiconductor region with respect to a first electrode contacting the substrate, by controlling the extension of a depletion layer formed at the pn junction Since the wavelength characteristics are variable, it is possible to detect light in different wavelength ranges with one element, and also to perform analog light detection over the entire range of wavelength ranges. is there.

[Brief description of the drawings]

FIGS. 1 (a) and 1 (b) show a wavelength characteristic variable photodiode according to a first embodiment of the present invention, and FIGS. 2 (a) and 2 (b) show each of the sensors. FIG. 3 is an explanatory diagram showing the expansion of a depletion layer in an operating state, FIG. 3 is a diagram showing an equivalent circuit of a color sensor according to a second embodiment of the present invention, and FIG. 4 is a timing chart of horizontal and vertical shift registers of the color sensor. FIGS. 5 and 6 are a plan view and a cross-sectional view taken along the line AA 'of the color sensor, respectively. 1 ...... n-type silicon substrate, 2 ...... p ⁺ diffusion layer, 3 ...... n ^-
Diffusion layer, 4 first electrode 4, 5 insulating film, 6 second electrode for control, 7 third electrode, 8 n ⁺ diffusion layer, TrV, TrH Switching transistor, 9 ... field insulating film, 10 ... channel stopper, 11 ... interlayer insulating film.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 31/10-31/119 H01L 27 / 14,27 / 15

Claims (2)

(57) [Claims] 1. A semiconductor substrate of a first conductivity type, a plurality of semiconductor regions of a second conductivity type arranged in an array on a surface of the semiconductor substrate at a predetermined interval, and a contact with each of the semiconductor regions A plurality of second electrodes formed on the substrate, a second electrode formed on the substrate in a region corresponding to each of the semiconductor regions, and a second electrode configured to contact the substrate. And a voltage supply device for applying a predetermined voltage between the first electrode and each of the second electrodes, and a current between the first electrode and the third electrode. Wherein a voltage applied to each of the first electrodes is configured to be different for each of the semiconductor regions, and pn formed between the semiconductor substrate and the semiconductor region. Controlling the extension of the depletion layer formed at the junction A photodetector for detecting light in a desired wavelength region for each semiconductor region, thereby enabling multicolor reading. 2. A semiconductor substrate of a first conductivity type, a plurality of semiconductor regions of a second conductivity type arranged in an array on a surface of the semiconductor substrate at a predetermined interval, and a contact with each of the semiconductor regions A plurality of first electrodes formed on the substrate, a second electrode formed on a part of the substrate at a position corresponding to each of the semiconductor regions, and a second electrode configured to contact the substrate. And a voltage supply device for applying a predetermined voltage between the first electrode and each of the second electrodes, and a current between the first electrode and the third electrode. Wherein the applied voltage to each of the second electrodes is made variable in a plurality of stages, so that the same region is read with a plurality of different applied voltages, and the semiconductor substrate and the semiconductor Formed in the pn junction formed between the regions A photodetector that performs multicolor reading by detecting light in a desired wavelength region each time by controlling the extension of a depletion layer.