Electron Device Incorporating A Microchannel Secondary Emitter

Abstract

An electron device incorporating a microchannel plate as a secondary emission electron source which in addition to the primary current provided by an electron emitter, such as a thermionic emitter, will provide high gains. By impressing the proper voltages thereon, the entrance and exit surfaces of the microchannel plate serve respectively as equivalents to the control grid and screen grid in a conventional type tube.

Description

BACKGROUND OF THE INVENTION

The invention described is directed to an electron device for obtaining voltage gain, oscillation, frequency mixing, detection, power transfer and for various other uses by utilizing the characteristics of the microchannel plate.

DESCRIPTION OF THE PRIOR ART

It is present practice in electron devices to use thermionic emitters as a sole source of electrons for the purpose of obtaining voltage gain, oscillation, frequency mixing, detection, power transfer and other purposes. The thermionic emitter is usually, but not necessarily, in the form of an indirectly heated cathode coated with mixture of carbonates, which when reduced provide electrons. Concentric with this cathode are located grids and anodes which provide the necessary control, suppression, focusing and collection of the electrons emitted by the thermionic emitter. A plurality of the electrons emitted by the cathode are collected by the anode or plate concentric with the cathode, while a minority of these electrons are collected by other electrodes such as the screen grid or other accelerating electrodes. For a given amount of electrons or current from the emitter, the efficiency or gain of an electron device is dependent upon the extent of change in plate (anode) current relative to the change of voltage impressed on the first or control grid. This is referred to as the transconductance (G.sub.M = dI.sub.b /dE.sub.ci) of the device; and the higher this characteristic the higher the gain of the device. To obtain higher levels of transconductance it has been common practice to utilize control grids which embody a large number of turns per inch of very fine wire (lateral wire) which permits large changes in electrons passing through or between these wires for very discrete changes in the voltage applied to them. For a device having a given control grid construction, the transconductance may be increased by increasing the number of electrons thus creating a higher level of current to be varied by the given control grid construction. This has the disadvantage of requiring an emitter of large physical size which is not always desirable, particularly in high frequency applications where interelectrode capacities become an important part of the required circuitry. Another disadvantage is that more power is required to bring the emitter up to the required temperature to obtain electron emission.

To acquire high values of G.sub.M, secondary emission has been employed to multiply the electron current after it has passed through the control grid. This has been done by deflecting the electrons (after passing through the control grid) onto appropriately treated surfaces at the appropriate angle of incidences where secondary electrons are generated and are subsequently collected by the anode. The transconductance or gain of these tubes is thus increased by a factor equal to the number of secondary electrons generated by each primary electron. If four secondary electrons are obtained for each primary the transconductances is increased by a factor of four. While this has the advantage of requiring smaller electron emitting surfaces to obtain very high values of transconductance, there are inherent disadvantages to this device, such as the much more complex mechanical construction, treatment and care in handling the secondary emission surfaces. Due to these and other disadvantages, this type of device has found limited usage.

SUMMARY OF THE INVENTION

It is the object of this invention to provide an electron device which will incorporate a microchannel plate as a secondary emission electron source which in addition to the primary current provided by an electron emitter, as for example, a thermionic emitter, will provide extremely high gains. It is a further object of this disclosure to utilize the conducting surfaces of the microchannel plate as the control and screen grid electrodes necessary for the proper functioning of the device.

The advantages of this invention are as follows:

1. The gain of the microchannel multiplied by the gain realized from using the input electrode as a control grid permits design of a device of enormous gain.

2. Use of the input microchannel electrode as a control grid and the output microchannel electrodes as a screen grid greatly simplifies the construction since electrodes are in perfect alignment; no grid adjusting is required and screen current (microchannel exit surface) is minimal.

3. Due to the large numbers of secondaries generated by the microchannel plate, the primary current can be low; in fact the lower the primary current the higher the microchannel gain since they have a tendency to saturate at higher current densities. A very low heater power is thus required to provide this minimal primary current density. It is conceivable that cold emitters might even be used to furnish the required current density.

4. Microphonics characteristics would also be improved due to the solid construction and the absence of flimsy wire parts incorporated in conventional tubes.

5. The lower heater power requirements reduces the power supply demands, hence increasing the portability of equipment incorporating these devices.

6. Construction is simplified making it more adaptable to automatic assembly procedures.

7. Since the gain is high, and the device may be made very small and compact, it is ideally suited for high frequency application.

BRIEF DESCRIPTION OF THE DRAWING

The drawing shows the arrangement of components for one contemplated embodiment of the disclosed invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the Figure, a thermionic emitter 11, for example, is used to provide the primary electrons. This emitter is of the planar type to permit uniform spacing with the microchannel plate 12. The entrance surface 13 of the microchannel plate 12 by being made conductive is used as the control grid and will permit electrons to enter or not, depending upon the potential impressed upon it by a voltage source V.sub.MCP . A signal to be amplified could also be added at this point. Since the tubes or channels of the microchannel plate 12 are very small, discrete changes in this voltage will result in large changes in primary electrons entering the microchannel. After the primary electrons pass through the entrance surface 13 they generate secondaries in the microchannel plate as is known in the art. The exit surface 14, being made an electrically positive surface in relation to the entrance surface 13, the electrons are accelerated from the exit surface to be collected by the anode 15. The exit surface 14 is thus performing the function of a screen grid in a conventional tube. The gains realized, however, are increased to very high values due to the secondary multiplication. Thus, if the gain of the microchannel is 10.sup.4, the overall gain would equal G.sub.M .times. 10.sup.4 ; G.sub.M in this case being that at the entrance surface 13.

A suppressor grid 16 with voltage V.sub.s is shown between the exit surface 14 and the anode 15 which has voltage V.sub.a applied thereto. The function of the suppressor 16 is to provide a negative going field to prevent anode secondary electrons from returning to the exit microchannel surface. Anode secondaries are those which are released from the anode surface by electrons impinging thereon from the microchannel exit surface. By selecting appropriate distances between the microchannel exit surface and the anode, the suppressor may not be required.

While only one embodiment of the contemplated invention has been described, it is to be understood that many variations, substitutions and alterations may be made while remaining within the spirit and scope of the invention which is limited only by the following claims.

Claims

I claim:

1. A high gain electron device comprising:

a planar surface electron source having means associated therewith for causing electrons to be emitted therefrom;

a microchannel plate having parallel conductive entrance and exit faces positioned proximate said surface with said entrance face and said planar surface in parallel relationship;

anode means positioned to receive electrons from the exit face of said microchannel plate;

means associated with said entrance face for receiving a modulating voltage;

means associated with said exit face for receiving a biasing voltage, whereby the voltages impressed upon said faces control the gain of the device by causing the entrance and exit faces to function as a control grid and screen grid respectively; and

a suppressor grid located between said exit face and anode for preventing anode electrons from returning to said exit face.

2. The high gain electron device according to claim 1 wherein said electron source and associated means comprise an indirectly heated planar thermionic emitter.