JP3654480B2 - Field emission photo-current converter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a field emission light-to-current converter that generates a high electric field at a sharp needle tip of a micro needle-shaped electron radiation source, irradiates light on the needle, emits electrons, and converts light into current. .
[0002]
[Prior art and problems to be solved by the invention]
The most widely used light-current converter is a photomultiplier, and a charge coupled device called a charge coupling device (CCD). The advantage of the photomultiplier is that it responds to extremely weak light and has a high amplification factor. The disadvantages are that the response speed is as low as microseconds, the conversion current is as small as microamperes, and the light intensity and current are also low. There is a variation in the correlation between and dark current and noise are high.
Also, the CCD does not directly convert light into an amount of current, but can convert light into electric charge once and then convert it into electric current at the reading stage. Accordingly, there is an advantage that the correlation between the light intensity and the amount of current is extremely high, but since the conversion process is in two stages, the response speed is slow and the mechanism is complicated.
[0003]
The present invention is also of the order to solve the above problems, and objectives can be high-speed response, and conversion current amount is large, to provide a field emission light over current converter capable of achieving low noise To do.
[0004]
[Means for Solving the Problems]
The field emission type photo-current converter of the present invention has an insulating or semi-insulating thin film formed on the surface thereof, and closely arranged micro needle-shaped electron radiation sources, and is opposed to the micro needle-shaped electron radiation source in the vicinity. A current measuring electrode connected to the current collecting electrode, and applying a voltage between the micro needle electron emission source and the current collecting electrode to generate a high electric field at the tip of the micro needle electron emission source. Irradiate light to the tip of the microneedle-shaped electron emission source to emit electrons from the surface, flow the emitted electrons through the current collection electrode, and generate a current corresponding to the intensity of the light flowing through the current collection electrode. It is characterized in that it is measured by a current measuring means.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
Field emission refers to a phenomenon in which a high electric field is generated at a sharp needle tip, thereby reducing a potential barrier against electrons confined in the surface of the needle tip and releasing electrons from the surface. In metal needles, the amount of radiated current greatly increases or decreases depending on the electric field strength at the needle tip. However, in semiconductors, especially semiconductors that are close to insulating, when the needle tip is irradiated with light, the photoelectric conductivity increases momentarily and the amount of current increases. Increase. This principle is applied to the light-current converter in the present invention.
[0006]
FIG. 1 is an explanatory view of a basic structure of a field emission type photo-current converter of the present invention.
In FIG. 1, insulating or semi-insulating microneedle electron emission sources 2 are densely arranged on a conductive substrate 1 forming an electron emission surface, and a current collecting electrode 3 is arranged facing this. Although the microneedle-shaped electron emission source 2 may be configured as a single needle such as a normal field emission microscope, when used in a converter, fine needles are densely formed in order to increase conversion efficiency. The size of each microneedle varies depending on the conversion efficiency and conversion response speed, but a height of several μm to several hundred μm is desirable. The interval between the needles is also widened to several μm to several hundred μm depending on the height of the needle. If the needle tip is sharp, the sharper one is desirable. When the tip is polished until the radius of curvature becomes 0.1 μm or less, a field emission current amount can be obtained at a low voltage (1000 V or less).
[0007]
The current collecting electrode 3 is disposed at a position several μm away from the tip of the microneedle-shaped electron emission source 2. A high voltage power supply 4 is connected between the conductive substrate 1 and the current collecting electrode 3, and the current flowing through the current collecting electrode 3 is measured by an ammeter 5.
[0008]
Next, the operation will be described. First, the high voltage power source 4 is several hundred volts depending on the distance between the microneedle electron emission source 2 on the electron emission surface and the current collecting electrode 3 and the radius of curvature of the microneedle electron emission source 2. A voltage of about several KV is applied so that a field emission current flows. Thereafter, light is irradiated onto the microneedle electron emission source. Then, the radiation current changes corresponding to the light intensity, the current flowing through the current collecting electrode 3 changes, and light can be converted into a current.
[0009]
FIG. 2 is a diagram showing another example of the light-current converter of the present invention.
[0010]
In this example, in order to further improve the conversion sensitivity with respect to the converter shown in FIG. 1, an extraction electrode 10 is provided facing the microneedle electron emission source 2, and a microchannel plate is provided in front of the current collection electrode 3. 12 is arranged. The extraction electrode 10 is a projection-shaped microelectrode in which a conical hole is formed so as to surround the tip of the microneedle electron emission source 2, and a piezoelectric element is used for alignment between the microneedle electron emission source 2 and the extraction electrode 10. 11 is used, and by applying a voltage to the piezoelectric element 11, alignment is performed so that the most current flows through the current collecting electrode 3. The extraction electrode 10 is formed by a method of forming a metal thin plate such as platinum by mechanically opening a hole with a fine punch, a method of applying a microlithography technique, or an electroforming method. A high voltage power supply 13 is inserted between the microchannel plate 12 and the current collecting electrode 3. Since a micro current is multiplied by the microchannel plate 12, the amount of current increases, but the structure becomes complicated. Therefore, an amplifier is provided between the current collecting electrode 3 and the ammeter 5 instead of the micro channel plate. It may be inserted.
[0011]
The current collecting electrode 3 is made of highly transparent sapphire or glass and covered with a conductive thin film such as a nesa film (film of tin oxide or the like). In this case, the wavelength range of light to which the converter responds varies depending on the light transmission characteristics of the Nesa film. Therefore, when the nesa film is used as a filter, a converter that responds to a specific wavelength can be configured.
[0012]
FIG. 3 is a diagram showing another example in which the conversion sensitivity of the photo-current converter is improved.
In this example, an extraction electrode plate 21 having a hole surrounding the tip of each microneedle-shaped electron emission source 2 is provided on a conductive substrate 1 via an insulator. A hole through which the needle-shaped electron emission source 2 passes is formed. A predetermined extraction voltage is applied between the microneedle electron emission source 2 and the extraction electrode plate 21.
With such a configuration, it is possible to reduce the voltage necessary for electron emission.
[0013]
In each of the above examples, since the fabrication of the densely arrayed microneedle-shaped electron emission source, the extraction electrode, and the current collection electrode requires microfabrication, it is manufactured by applying vacuum microelectronics and microlithography technologies that have made remarkable progress in recent years. .
[0014]
For the electron emission source, metal has no photoconductive effect, and an insulating or semi-insulating material is used. Silicon is considered the best material because of advanced microfabrication techniques, but is not desirable because the electron emitting surface is unstable. Diamond has a stable emission surface and an excellent electron emission effect. However, it is difficult to produce fine diamond needles.
Therefore, as shown in FIG. 4, a densely arranged fine needle-shaped radiation source 2 is made of silicon or metal, and the surface thereof is carbonized, oxidized, or nitrided with diamond or semi-insulating or insulating and photoconductive base metal. It is possible to form a stable electron source by forming a thin film 2a.
[0015]
In this case, the light-current conversion characteristics vary depending on the conductivity, thickness, composition, and structure of the carbonized film, nitride film, oxide film, diamond film, etc. at the emission region at the tip of the fine needle-shaped electron radiation source. Of particular interest is the wavelength range of response light and the response time.
[0016]
FIG. 5 shows the light irradiation time and the waveform of the radiation current that responds. The light irradiation time width ranges from nanoseconds to femtoseconds. In the converter that responds to this light pulse, the light-current conversion of the insulating thin film material is performed. And the thickness of the film is required to be uniform and several nanometers.
[0017]
The time difference between the light pulse and the radiation current is a time delay in the light-current converter and the measuring device. When the light irradiation amount is weak and the irradiation time width is narrow, the radiation current is attenuated and cannot be detected. It also depends on the wavelength of light. Therefore, it is possible to make a photo-current converter that responds only to a specific wavelength pulse width.
[0018]
【The invention's effect】
As described above, according to the present invention, a high electric field is generated at the sharp needle tip of a fine needle-shaped electron radiation source having an insulating or semi-insulating thin film formed on the surface, and light is applied to the needle tip. A current corresponding to the intensity of light can be taken out from the opposing current collecting electrodes, and can be applied to a photo-electrode converter.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic structure of a field emission type photo-current converter.
FIG. 2 is a diagram showing another example of the photo-current converter.
FIG. 3 is a diagram showing another example in which the conversion sensitivity of the photocurrent converter is improved.
FIG. 4 is a diagram for explaining a method of manufacturing a fine needle-shaped radiation source.
FIG. 5 is a diagram showing a light irradiation time and a waveform of a radiation current that responds.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Conductive board | substrate, 2 ... Micro needle-shaped electron emission source, 3 ... Current collection electrode, 4 ... High voltage power supply, 5 ... Ammeter, 10 ... Extraction electrode, 11 ... Piezoelectric element, 12 ... Microchannel plate, 13 ... High voltage power source, 20 ... insulator, 21 ... extraction electrode plate.

Claims (2)

Insulating or semi-insulating thin film formed on the surface, closely arranged micro-needle electron radiation source, current collecting electrode arranged in close proximity to the micro-needle electron radiation source, and connected to the current collecting electrode Current measuring means, and a voltage is applied between the microneedle electron emission source and the current collecting electrode to generate a high electric field at the tip of the microneedle electron emission source, and the tip of the microneedle electron emission source Irradiates light from the surface, emits electrons from the surface, flows the emitted electrons through the current collection electrode, and measures the current according to the intensity of the light flowing through the current collection electrode with a current measuring means. -Current converter.   2. The field emission type photo-current converter according to claim 1, wherein an extraction electrode is provided at the tip of the fine needle-shaped electron radiation source.

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