CN102280332B - MIPM (multum in parvo mapping)-type internal field emitting cathode - Google Patents

Abstract

The cathode of the invention belongs to the field of vacuum electronics and material science, and in particular relates to a MIPM type internal field emission cathode. The MIPM internal field emission cathode of the present invention is composed of a bottom electrode layer, an insulating layer, an electron storage and transport layer and a top electrode layer, and its main feature is that the electron storage and transport layer adopts porous silicon film material. In the AC driving mode, the functional layer can not only transport electrons but also store electrons, thereby improving emission efficiency. Compared with the prior art, the invention has the advantages of large emission current, good stability, etc., and the cathode environment adaptability is strong, and it can not only work in gas, but also work in liquid.

Description

A MIPM type internal field emission cathode

technical field

The invention belongs to the field of vacuum electronics and material science, in particular to an MIPM type internal field emission cathode.

Background technique

There are three types of field electron emission: one is external field emission, the other is internal field emission, and the third is transverse field emission. the

External field emission cathodes are made of metal or semiconductor cones, nanotubes, nanowires, etc. The principle is to use an external strong electric field to suppress the surface barrier, reduce the highest point of the barrier, and narrow the width of the barrier. When the width of the barrier on the surface of the cold cathode is compressed by the electric field to be comparable to the wavelength of electrons, a large number of electrons escape through the surface barrier due to the tunneling effect of electrons. The principle of lateral field emission is to use the conduction current of discontinuous film or nano-slit to form electron emission and be drawn out by vertical electric field, also known as surface conduction cathode. The principle of internal field emission is to use the internal strong field to make electrons enter the dielectric layer from the substrate, and accelerate in the dielectric layer to obtain enough energy to escape the dielectric layer. Since the built-in electric field of the internal field emission cathode is not affected by the external atmosphere, the internal field emission is not sensitive to surface morphology and gas adsorption. At present, the internal field emission cathode can be divided into three types from the structure and principle: one is the metal-insulator-metal (Metal-Insulator-Metal, MIM) type, and the other is the metal-porous silicon-metal (MPM) type. ) Metal-Porous Silicon-Metal (MPM) type, and the third type is Metal-Insulator-Semiconductor-Metal (Metal-Insulator-Semiconductor-Metal, MISM) type. the

When electrons pass through the insulating layer of the MIM cathode, the electrons will lose most of their kinetic energy due to scattering, resulting in most of the electrons not being emitted from the top metal electrode, so the emission efficiency of the MIM cathode is not high. The MPM type was proposed by Nobuyoshi Koshida et al. in Japan in 1995 (Jpn. J. Appl. Phys. Vol. 34,1995, pp. L705-L707). There are a large number of nano-silicon grains in porous silicon, and when electrons pass through it, due to the quantum tunneling effect, the energy loss is relatively small. Compared with the MIM type, the gate operating voltage of this MPM type cathode can be reduced to less than 20 V, and its cathode electron emission efficiency currently exceeds 10%, but the emission efficiency is not stable. A kind of MPM type cathode recently reported in Japan, the gate voltage is 16 V, and the emission efficiency drops from 2.1% to 1.6% after working for 5 hours, and the drop rate is 23%.

The MISM type cathode is driven by alternating current, and its working principle is as follows: in the negative half cycle of the alternating current driving voltage, the potential of the lower electrode is positive, and electrons are injected from the upper electrode to the interface between the semiconductor layer and the insulator layer, and exist on the interface in the form of interface state electrons. . When the voltage is reversed, the electrons on the interface return to the semiconductor layer, where they are accelerated, and then enter the upper electrode, and some electrons with high energy can overcome the surface barrier of the upper electrode and emit into the vacuum. The advantage of this kind of cathode is that the stability of electron emission is good, but the disadvantage is that the emission efficiency is not high. The domestic patent (application number 01140447.7, authorized announcement number CN 1142572C) has improved the semiconductor layer in this structure (referred to as the electron transport layer in this patent), using a gradual change from a high electron affinity component to a low electron The thin film of the component of the affinity is used as a semiconductor layer, and the emission efficiency exceeds 0.5%, but the emission efficiency still cannot meet the needs of practical applications (such as field emission flat panel displays), and its performance still needs further improvement.

Contents of the invention

A technical problem to be solved by the invention is the disadvantages of low emission efficiency and low emission current density of the existing MISM type internal field emission type cathode.

In order to solve the above problems, the present invention replaces the common semiconductor layer in the MISM type cathode with porous silicon to form a MIPM type (Metal-Insulator-Semiconductor-Metal, metal-insulator-porous silicon-metal) internal field emission cathode, from From bottom to top, it includes four functional thin film layers that are closely combined: bottom electrode layer 1, insulating layer 2, electron storage and transport layer 3 and top electrode layer 4. It is characterized in that the material of the bottom electrode layer is metal or alloy, and the thickness ≧10 nm, the material of the top electrode layer is metal, alloy, doped diamond-like carbon or semiconductor with low electron affinity potential energy, the thickness is 5 nm~500 nm, the material of the insulating layer is metal oxide, the second Group IV element oxides, ceramics or mica, with a thickness of 100 nm to 1 μm, and the electron storage and transport layer material is n-type porous silicon, with a thickness of 10 μm to 500 μm.

Described MIPM type internal field emission cathode is characterized in that, the average conductivity of described n-type porous silicon is 0.005 Ω × cm ~ 3 Ω × cm, the average porosity is 5% ~ 80%, and the average pore size is 1 nm~100μm.

When the cathode is driven by AC and works in the negative half cycle, that is, when the potential of the lower electrode is positive, for the traditional MISM type internal field emission cathode, electrons are injected from the upper electrode to the interface between the semiconductor layer and the insulator layer, and the electrons in the interface state The form exists on the interface; for the MIPM type internal field emission cathode provided by the present invention, electrons can be stored not only on the interface between the semiconductor layer and the insulator layer but also in the porous silicon layer, thereby ensuring the efficiency and the density of the emission current. This is because the grain boundaries of nanocrystals that exist in large quantities in porous silicon can trap a large number of electrons, and porous silicon can be "charged" when working under an AC negative bias. When the working voltage is reversed, the electrons are driven by the internal field to form a large current emission. This working mode not only ensures the emission efficiency of the internal field emission cathode, but also ensures the stability of the work. This internal field emission cathode can not only work in liquid, atmosphere or vacuum, but also work in extreme conditions such as high temperature and high radiation.

Description of drawings

Figure 1 Schematic diagram of the structure of the MIPM type internal field emission cathode.

Detailed ways

The present invention will be further described below in conjunction with accompanying drawing.

Example 1

Referring to Fig. 1, the material of the bottom electrode 1 is gold with a thickness of 500 nm; the material of the insulating layer 2 is SiO ₂ with a thickness of 100 nm; the material of the electron storage and transport layer 3 is porous silicon with a thickness of 40 μm. The average conductivity is 0.01 Ω, the average porosity is 50%, and the average pore diameter is 30 nm; the material of the top electrode 4 is gold, and the thickness is 15 nm. Under the pressure of 10 ^-5 torr, the measured emission efficiency is 1.5%, and the beam decays by 1% after 20 hours of continuous operation.

Example 2

Referring to Fig. 1, the material 1 of the bottom electrode is chromium with a thickness of 200 nm; the material of the insulating layer 2 is HfO ₂ with a thickness of 300 nm; the material of the electron storage and transport layer 3 is porous silicon with a thickness of 40 μm. The average conductivity is 0.01 Ω, the average porosity is 50%, and the average pore diameter is 50 nm; the material of the top electrode 4 is Ag, and the thickness is 10 nm. Under the pressure of 10 ^-5 torr, the measured emission efficiency is 1.5%, and the beam decays by 1% after 20 hours of continuous operation.

Example 3

Referring to Fig. 1, the material of the bottom electrode 1 is Ag with a thickness of 200 nm; the material of the insulating layer 2 is Ta ₂ O ₅ with a thickness of 400 nm; the material of the electron storage and transport layer 3 is porous silicon with a thickness of 30 μm , with an average conductivity of 0.01 Ω, an average porosity of 50%, and an average pore diameter of 30 nm; the top electrode 4 is made of ZrN with a thickness of 8 nm. Under the pressure of 10 ^-5 torr, the measured emission efficiency is 1.3%, and the beam decays by 1% after 20 hours of continuous operation.

Claims (2)

1. a kind of MIPM type internal field emission negative electrode, it comprises four functional film layers connected successively: bottom electrode layer, insulating layer, electron storage transport layer and top electrode layer, it is characterized in that, described bottom electrode layer material is Metal or alloy, thickness ≧ 10 nm, the material of the top electrode layer is a metal or semiconductor with low electron affinity potential energy, the metal or semiconductor with low electron affinity potential energy is Au, Ag or ZrN, and the thickness is 5 nm ~500 nm, the material of the insulating layer is metal oxide, group IV element oxide, ceramic or mica, with a thickness of 100 nm~1 μm, and the material of the electron storage and transport layer is n-type porous silicon, with a thickness of 10μm~0.5mm. 2. MIPM type internal field emission cathode as claimed in claim 1, is characterized in that, the average conductivity of described n-type porous silicon is 0.005 Ω * cm ~ 3 Ω * cm, and average porosity is 5% ~ 80 %, the average pore size is 1 nm~100 μm.

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