JPH04324980A - Electrostatic field detector element and electrostatic field measuring device - Google Patents

Abstract

PURPOSE:To enable an electrostatic field or an electrostatic field profile to be accurately and quickly measured by a method wherein a source diffusion layer and a drain diffusion layer different from a substrate in conductivity type, an electrically floating gate electrode formed on a thin oxide film, and a dielectric film are provided. CONSTITUTION:A source diffusion layer 2 and a drain diffusion layer 3 different from a substrate 1 in conductivity type are formed on the substrate 1. The gate electrode of an electrostatic electrode is composed of a polycrystalline Si film 4 and an Al film 5 and made to stay in an electrically floating state. A dielectric film 6 is used for converging an electric field, and a thin oxide-film 7 is interposed between the gate electrode and the substrate 1. The thickness of the gate electrode is set much larger than that of the thin oxide film 7. A thick field oxide film 8 is formed to isolate adjacent elements from each other. By this setup, an electrostatic field and the distribution of an electrostatic field can be easily and quickly detected high in degree of resolution.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] There is an increasing need to measure static electricity images or profiles in copying machines, antistatic devices, and the like. The present invention relates to an element and a device that make it possible to measure an electrostatic field or a profile of an electrostatic field non-destructively, at high speed, and with high precision using semiconductor technology.

0002

2. Description of the Related Art Conventional electrostatic field measuring devices include electroscopes and electric balances. In these, the charge distribution on the detector electrode changes due to an electrostatic field, and the resulting Coulomb force is indicated by a pointer. These are just meters and cannot be taken out as electrical signals. Furthermore, since the detection unit is large, it is not possible to measure the spatial distribution of the electrostatic field. Recently, LiNbO3 and BSO (Bi12S
Electric field sensors that utilize the electro-optic effect of optical crystals such as iO20) and electric field sensors that utilize changes in the orientation of liquid crystals due to electric fields have been reported. In other words, these convert the change in light transmittance of the sensing element due to the electrostatic field into an electrical signal, and can measure the spatial distribution of the electrostatic field, but they require a light source and an image sensor in addition to the sensing element described above. The equipment is complicated and large.

0003

The conventional electrostatic measuring device or electrostatic field sensor has a large detecting section and cannot measure the distribution of the electrostatic field with high resolution. In other words, in electric field sensors that use the electro-optic effect of optical crystals and electrostatic field sensors that use the alignment phenomenon caused by the electric field of liquid crystals, it is the optical properties of these materials that respond to the electric field, and in order to extract them as electrical signals, further processing is required. A light source and an image sensor are required. Therefore, as the detection unit becomes larger, measurement errors tend to increase because two conversion processes are required: from electric field to transmittance and from transmittance to electric signal.

0004

[Means for solving the problem] An electrostatic field detection element has a source formed on a semiconductor Si substrate and has a conductivity type different from that of the substrate.
A drain diffusion layer, an electrically floating gate electrode formed on a thin oxide film interposed between both diffusion layers,
It consists of a dielectric film formed on the gate electrode. The thickness of the gate electrode is made sufficiently thicker than the oxide film directly under the gate. The dielectric film focuses the electric field onto the gate electrode, and is made of a material with a high relative dielectric constant.

The electrostatic field detection device includes a first common line connecting the drains of the electrostatic field detection elements arranged at a constant pitch, a field effect transistor connected to the source of the electrostatic field detection elements, and a field effect transistor connected to the source of the electrostatic field detection elements. A second common line to which the sources of the transistors are connected, and a control means for controlling the application of voltage to the gate electrode of the field effect transistor, and the signal current generated by the electric field detection element is sequentially connected to the first or second common line. It is output from the line.

[0006]

[Operation] When the floating gate electrode of the electrostatic field detection element is in an electric field, the charges in the gate electrode are polarized on the front and back surfaces. Since the thickness of the gate electrode is sufficiently thicker than the oxide film directly under the gate, the semiconductor surface directly under the gate is more strongly influenced by the charge on the back side of the gate, that is, the oxide film side of the gate, and the conductivity of the semiconductor surface is reduced by the action of the electric field. The type is reversed and conduction occurs between the source and drain. Conduction resistance is a function of an external electrostatic field, and if a constant voltage is applied between the drain and source, a detection signal can be output as a signal current when the electrostatic field exceeds a certain threshold. In order to detect the electrostatic field as an analog value, the semiconductor surface directly under the gate should be of a depression type, thereby making it possible to output a signal current proportional to the electric field. The dielectric film placed on the gate electrode has the effect of converging the electric field, so it is possible to detect the electrostatic field with high sensitivity.

The electrostatic field detection device can sequentially obtain signals corresponding to the distribution of the electrostatic field from the second common line in time series by applying a voltage from the control means to the gate electrode of the access field effect transistor. can.

Furthermore, by reducing the area of the electric field detection element using integrated circuit technology, the distribution of the electrostatic field can be detected with extremely high resolution and high precision.

[0009]

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

FIG. 1 is a sectional view (a) and a plan view (b) of an electrostatic field detection element according to an embodiment of the present invention. A source diffusion layer 2 and a drain diffusion layer 3 having a conductivity type different from that of the semiconductor substrate 1 are formed on the substrate. The polycrystalline Si film 4 and the Al film 5 form the gate electrode of the electrostatic field detection element,
Electrically, it is in a floating state. The dielectric film 6 is for converging the electric field. A thin oxide film 7 is interposed between the gate electrode and the substrate 1. The thickness of the gate electrode is made sufficiently larger than the thickness of the thin oxide film 7. A thick field oxide film 8 is formed to isolate adjacent devices. The wiring Al film 9 applies voltage to the source diffusion layer 2 and drain diffusion layer 3. Passivation film 10 protects the substrate.

In this embodiment, since an example is shown in which an electrostatic field in the positive direction is detected, the conductivity type between the source and drain is N-channel, the substrate is P-type, and the source and drain are N-type.

The polycrystalline Si film 4 is formed by a CVD method similar to the well-known MOS process, and the Al film 5 is formed by a vapor deposition method. The dielectric film 6 is made of a ferroelectric film such as Si nitride, BiTiO3, or PZT, and is formed to cover the gate electrode. In order to increase the electric field convergence effect, it is better to have a large dielectric constant and be thick.

When the electrostatic field detection element is inserted into a static electric field with the gate electrode facing forward, the charges in the gate electrode are polarized on the front and back surfaces. Since the thickness of the gate electrode is sufficiently thicker than the oxide film directly under the gate, the semiconductor surface directly under the gate is more strongly affected by the charge on the back side of the gate, that is, the oxide film side of the gate.
Due to the effect of the electric field, the conductivity type of the semiconductor surface is reversed and conduction occurs between the source and drain.

In the case of the enhancement type, the conductance between the source and drain increases as a function of the electric field due to polarized charges above a threshold electric field determined by various characteristics of the semiconductor and oxide film. It is non-conductive below the threshold electric field.

On the other hand, in the case of the depletion type, conduction occurs between the source and drain even in a zero electric field, and the conductance increases as the electric field increases, allowing the strength of the static electric field to be detected in an analog manner. By applying a constant bias voltage between the source and drain, a signal current proportional to the electrostatic field can be obtained from the source or drain terminal.

[0016] Hereinafter, the electrostatic field measuring device will be explained. FIG. 2 is a circuit block diagram of an electrostatic field measuring device that is an embodiment of the present invention. The electrostatic field measuring device consists of a plurality of static electric field detection elements 11 (11
a to 11e), access field effect transistor 12
(12a-12e), the first line 13 connected to the power supply
, a second common line 14 formed by commonly connecting the source electrodes of field effect transistors for access, and a scanning circuit 15 serving as a control means.

One electrode of each electrostatic field detection element 11 is connected to the first electrode.
The other electrodes are respectively connected to the drains of the access field effect transistors 12 to the common line 13 . The output terminal of the scanning circuit 15 is connected to the gate electrode of the field effect transistor 12 for access, and the output terminal of the scanning circuit 15 is connected to the gate electrode of the field effect transistor 12 for access.
It is possible to sequentially output the detection signals from the signal output terminal consisting of the second common line 14.

All of these elements can be formed at high density on a semiconductor substrate using integrated circuit technology, and
Resolutions higher than DPI are also possible. FIG. 3 is an operation timing chart of the electrostatic field measuring device.

The operation of the electrostatic field measuring device of this embodiment will be explained with reference to FIGS. 2 and 3. When the clock pulse CK and start signal ST are applied, the scanning circuit 15 operates and outputs scanning signals Y1, Y2, to Yn from its output terminal, thereby causing the access field effect transistor 1
2 are sequentially conductive, and the electrostatic field detection element 11 connected thereto.
A signal current Is appears on the signal output line.

Note that in FIG. 2, the first common line 1
3 is connected to the power supply line and the output signal is taken out from the second common line 14, but it is also possible to connect the second common line 14 to the ground and take out the output signal from the first common line 14. be.

[0021] Since the devices constituting this apparatus can be composed of Si devices, they can be operated at extremely high speeds.

[0022]

According to the present invention, it is possible to detect an electrostatic field and the distribution of an electrostatic field very simply, at high speed, and with high resolution, and its industrial effects are extremely large.

[Brief explanation of drawings]

FIG. 1 (a) is a cross-sectional view of an electrostatic field detection element of the present invention (b
) is a plan view of the electrostatic field detection element of the present invention.

[Figure 2] Block diagram of the electrostatic field measuring device of the present invention

[Figure 3] Operation timing chart of the electrostatic field measuring device of the present invention

[Explanation of symbols]

1 Semiconductor substrate 2 Source diffusion layer 3 Drain diffusion layer 4 Polycrystalline Si film 5 Al film 6 Dielectric film 7 Thin oxide film 11a Silent electric field detection element 11b Silent electric field detection element 11c Silent electric field detection element 11d Silent electric field detection element 11e Silent electric field detection element 12a Field effect transistor 12b Field effect transistor 12c Field effect transistor 12d Field effect transistor 12e Field effect transistor 13 First common line 14 Second common line 15 Scanning circuit

Claims (7)

[Claims] 1. Source and drain diffusion layers formed on a semiconductor substrate and having a conductivity type different from that of the substrate, a thin oxide film interposed between these two diffusion layers, and an electrically conductive layer formed on the thin oxide film. An electrostatic field detection element including a floating gate electrode and a dielectric film formed on the gate electrode. 2. The electrostatic field detection element according to claim 1, comprising a gate electrode made of a laminated film of Al or polycrystalline Si and Al, and having a thickness sufficiently larger than that of a thin oxide film. 3. The electrostatic field detection element according to claim 1, wherein a conductive channel is formed between the source and drain diffusion layers in a state where an external electric field is zero. 4. The dielectric film according to claim 1 is made of BiTiO.
3. Electrostatic field detection element made of ferroelectric material such as PZT. 5. At least one electrostatic field detection element according to claim 1, a first common line connecting the drain of the electrostatic field detection element, and an electric field connecting the source of the electrostatic field detection element to the drain. An electrostatic field detection device comprising an effect transistor, a second common line connecting the source of the field effect transistor, and control means for controlling application of a voltage to a gate electrode of the field effect transistor. 6. The electrostatic field detection device according to claim 5, comprising a first common line connected to a power supply voltage and a second common line outputting a signal current of the source of the electrostatic field detection element. 7. The electrostatic field detection device according to claim 5, comprising a second common line connected to a ground potential and a first common line that outputs a signal current of the source of the electrostatic field detection element.