JPS5912033B2 - solid state detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solid-state detector using a field effect transistor (hereinafter referred to as FET), which detects the photoinduced potential of a polymer thin film containing an organic photochromic material using the FET.
The present invention provides a device that amplifies and detects changes in the source/drain current of an ET.

Conventionally, MOS-FETs have also been used as phototransistors, and have been used as photoelectric conversion devices using current generated by the generation of electron-hole pairs in the gate portion by light.

However, such a detector using a MOS-FET does not have sufficient sensitivity, and its spectral sensitivity has not been particularly satisfactory. A photochromic material is a material that exhibits a reverse hue change due to the action of light.The hue change of an organic photochromic material due to light is due to a chemical change in its molecular structure. This often results in geometric changes in the molecular structure.

The principles of photochromism can be broadly classified into the following 15 six principles. (1) Isomerization, (2) Tautomerism, (3)
Ionic dissociation, (4) radical dissociation, (5) redox, (
6) Excited state change. A thin polymer film in which an organic compound exhibiting photochromism is dispersed or copolymerized in a polymer generates an induced potential when irradiated with light.

This is due to the fact that the photochromic portion in the polymer thin film changes according to the principle described above, and the charge density within the polymer thin film changes. This change in charge density is
(1) above, cases induced by geometric changes in the molecular structure (such as odors), and cases (3) to (6) where chemical changes that directly change the charge density occur. Specific organic photochromic materials include (1
) anils, (2) hydrazones, (3) semicarbazones, (4) triphenylmethane dyes, (5)
Examples include spiro compounds typified by various spiropyrans, (trans)other stilbene derivatives, thiosulfonates, cytosones, stilbene derivatives, formazanes, P-aminoazobenzene derivatives, thioindigo dyes, chloroph-35yl, and the like.

Among these, spiropyran is a typical example. A polymer thin film containing spiropyran changes the charge density in the film due to photochromism of spiropyran in the thin film when irradiated with light. Generates a large induced potential ranging from 10 millivolts to 1V.

The induced potential varies greatly depending on the polymer matrix containing this spiropyran. Polymers crosslinked (copolymerized) with spiropyran exhibit photodynamic phenomena [G. SmetsandF. B
lauwe}PureApplChem39 (1/2)
225 (1974)], and in this case, it has been shown that light irradiation causes reversible contraction of several percent or more in the polymer. This is due to a structural change in the photochromic part within this polymer.
This suggests a change in the charge density within the film due to light,
This change naturally generates a photoinduced potential. This photoinduced potential due to photochromism has the advantage of being able to detect light with various wavelength sensitivities due to the differences in spectral sensitivity of various organic photochromic materials, and providing a device that selectively detects the wavelength of light. are doing. Furthermore, when using photochromism based on photoisomerization such as a stilbene derivative, isomerization of the sheath trans occurs with light of two different wavelengths, and each state is memorized. In the case of photochromism having such a bistable memory function, the present invention is useful not only for light detection but also as a device for optical information storage. The polymer matrix containing the organic photochromic material may be copolymerized with the photochromic material, or a polymer matrix with good compatibility may be selected.

This compatibility can be easily achieved by choosing a polymer with a similar structure to the photochromic material or a polar polymer. In any case, a polymer matrix that generates a large photoinduced potential is preferable, and a polymer that is soft, has high insulation resistance, and whose charge density easily changes is preferable. The polymer thin film layer that generates these photoinduced potentials is formed as follows.

Namely, there are (1) a method in which the above-mentioned polymer composition is dissolved and dispersed in a solvent and a thin film is formed on the gate portion by spinner spraying or the like, and (2) a vapor phase method using methods such as plasma polymerization and sputtering. On the other hand, as is well known, F
The basic operation of an ET is to control the source/drain current by the electric field at the gate.

The present invention uses this FET, and FIG. 1 shows a solid state detector according to an embodiment of the present invention.
In the figure, 1 is an n-type semiconductor silicon substrate, 2 and 3 are P-type source and drain regions formed in the substrate 1, and 4 is an insulating layer made of SiO2 etc. formed on the substrate 1, which is an organic polymer layer. It is intended to avoid direct contact with the substrate surface and apply only the electric field effect to the gate portion of the FET, and has a thickness of, for example, several hundred to several thousand amps. Note that this insulating layer 4 is formed by oxidation or CVD, and is made of SiO.
2, Si, N4 film, or a multilayer structure thereof. Reference numeral 5 denotes an organic polymer layer that is placed on the insulating layer 4 and includes a photochromic material that generates an induced potential by light.

Now, when the organic polymer layer 5 is deposited on the gate via the insulating layer 4, the potential of the organic material in the organic polymer layer 5 changes depending on the wavelength and amount of the irradiated light. As a result, a change occurs in the drain current. By the way, there are two types of FETs: P-channel type and N-channel type.
Below 0, where there is an n-type, the explanation will be based on the configuration shown in FIG.

FET drain current 1.

is known to be given by: in the unsaturated region and in the saturated region.

Here, μ: mobility, EOx: dielectric constant of an insulating layer such as SiO2 film, EO: dielectric constant of vacuum, W: channel width,
L: length of channel, TQX: thickness of insulator layer such as SiO2, VD: drain voltage. Since there is no gate electrode in the configuration of the present invention as shown in FIG. 1, the threshold voltage VT used in the above equations (1') and (2) is given by the following as a first approximation.

Here, the capacitance due to an insulating layer such as CO:SiO2 film,
φf: Fermi potential in the silicon substrate,
For example, what is the impurity concentration of n-type silicon substrate 1? is 1015
/1, it becomes -0.29V. Q8S is a fixed charge generated at the interface between the insulating layer 4 and the silicon substrate. For example, if the insulating layer 4 is a SiO film, for example, in the case of a 111 silicon substrate, +8.0X10-8
C0u10mbZj. QB is n-type silicon substrate 1
In the case of a P-channel FET using

Here, Xdmax is the depletion layer width, ESi is the dielectric constant of silicon, and q is the unit charge. Here, CO=3.5×1
0-8F/c woman, Qss2+8.0×10-8C0u1
0mb/i1φf-10.29, exposure=1.4×10-8
If C0u10mb/Cd, then from equation (3), 23.2
It becomes 6V. Therefore, in this case, the P channel type E
It can be seen that enhancement type operation is performed. Drain current 1. V to flow. Since is negative, it is necessary to make it a negative voltage as is clear from equation (g). In FIG. 1, if the charge generated at the interface with the insulating layer 4 by the light irradiated on the organic polymer layer 5 is 1Q, it can be given by υ. .

The value of I changes, and P channel 7 is generated, and accordingly, as is clear from equations (1') and (2), I. will change. However, in the above explanation, it is assumed that there is no ionized charge in the insulator layer 5, but
In some cases, it may be necessary to consider the effect of ionized charges. Furthermore, FIG. 2 shows a solid state detector according to another embodiment of the present invention, which does not have an insulating layer 4 and in which an organic polymer layer 5 directly contacts the surface of a silicon substrate 1 corresponding to a gate portion. be. In this case, the reliability and lifespan are slightly inferior to the case shown in FIG. 1, but light sensing is still possible. In the device shown in FIG. 2, electrons are exchanged between the organic polymer layer 5 and the substrate 1, and the drain current of the FET changes. FIG. 3 shows still another device of the present invention, in which an electrode 8 is provided on an insulating layer 4, and an organic material layer 5 is provided on the insulating layer 4.
, and the electrode 8 is grounded via a high resistance R9. If the resistance value of R is low, the potential change of the organic material layer 5 will be grounded, but if the most resistive material is used, the material layer 5 will be grounded.
The FET responds instantaneously (the FET has a μSec response) to a potential change, causing a change in the drain current. Furthermore, the method for mounting the semiconductor chip of the present invention is the same as that for general phototransistors, and may be molded in a transparent plastic package. Next, examples of the present invention will be described.

Example 1 Fine powder of 3,3,3-trimethylintri-1-6'-nitrobenzospiropyran 3501), 60% uncured epoxy resin varnish, and 5% carbon black were dissolved and dispersed in methyl ethyl ketone to prepare a paint. Using a spinner, it was applied to the gate portion of an enhancement type MOS FET formed on a silicon single crystal wafer and cured.

The film thickness was approximately 0.5 μm. After metal vapor deposition on each electrode part of this chip, it was fixed on a stem and bonded with a 25 μm Au wire to produce a device as shown in FIG. -V.O.
Apply = -3V and use a light source with a color temperature of 2854A for 20
When irradiated with light at the illuminance of Lux, the dark current was 0.
A large photocurrent of about 1.4 mA was obtained for 1 μA. The paint used in this example was applied to a thickness of about 1 μm on a metal plate, and the film potential was measured by illuminating it with light in the same manner as above. ~620m
potential was measured. As described above, in the solid state detector according to the present invention shown in FIGS. 1 to 3, there is no restriction on the resistance value of the organic polymer layer 5, and the resistance value can be increased.

In other words, the output impedance between the source and drain is much smaller than the human input impedance between the gate and source, so it has the great advantage of being able to convert the impedance and amplify the detected current. It is. In addition, the present invention allows for the creation of sensors with various spectral sensitivities that reflect the various molecular structure differences of organic photochromic materials, corresponding to the light wavelength sensitivity of the photochromic materials, and also provides optical information of the photochromic materials. Signals corresponding to accumulation can be extracted electrically.

Further, by using the detection device (sensor) of the present invention as a planar sensor arranged in a planar array, a wide range of applications such as an image sensor or a multi-detector in which each detector has a spectral sensitivity can be considered.

The monolithic image sensor according to the present invention is extremely small and can be provided with a special spectral sensitivity by arbitrarily selecting the photochromic material, and can be used as a color image sensor or an ultraviolet sensor in industrial applications. It is available.

[Brief explanation of the drawing]

1 to 3 are schematic structural cross-sectional views of solid-state detectors according to embodiments of the present invention, respectively. 1... Silicon semiconductor substrate, 2, 3...
・Source/drain region, 4...Insulating layer, 5.
...organic polymer layer containing photochromic material,
6...Light, 8...Electrode, 9...
・High resistance body.

Claims (1)

[Claims] 1. A thin polymer film layer in which an organic photochromic compound is dispersed or copolymerized is formed in a portion corresponding to the gate of a field effect transistor, and a photochromic compound is induced by light irradiated onto the thin polymer film layer. A solid-state detection device characterized in that a change in potential of the molecular thin film layer is detected as a change in source and drain current of the field effect transistor. 2. The solid state detection device according to claim 1, wherein the organic photochromic compound is a spiropyran derivative. 3. The solid-state detection device according to claim 1, wherein the polymer thin film layer and the field effect transistor are arranged in a planar manner.