# US 6,294,858 B1 · Microminiature thermionic converters

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- Number: US 6,294,858 B1
- Document ID: US6294858B1
- Status: Granted
- Kind: B1
- Application number: 09/257,335
- Filed: 1999-02-25
- Granted: 2001-09-25
- Earliest claimed: 1998-02-26
- Assignees: Sandia Corporation
- Inventors: Donald B. King; Laurence P. Sadwick; Bernard R. Wernsman
- Web page: https://patentgrep.com/patent/US6294858B1

## CPC

- H01J 45/00: Discharge tubes functioning as thermionic generators {(structural combination of fuel element with thermoelectric element G21C3/40; nuclear power plants using thermionic converters G21D7/04; structural combination of a radioactive source with a thermionic converter, e.g. radioisotope batteries G21H1/10; generators in which thermal or kinetic energy is converted into electrical energy by ionisation of a fluid and removal of the charge therefrom H02N3/00)}
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)

## Abstract

Microminiature thermionic converts (MTCs) having high energy-conversion efficiencies and variable operating temperatures. Methods of manufacturing those converters using semiconductor integrated circuit fabrication and micromachine manufacturing techniques are also disclosed. The MTCs of the invention incorporate cathode to anode spacing of about 1 micron or less and use cathode and anode materials having work functions ranging from about 1 eV to about 3 eV. Existing prior art thermionic converter technology has energy conversion efficiencies ranging from 5-15%. The MTCs of the present invention have maximum efficiencies of just under 30%, and thousands of the devices can be fabricated at modest costs.

## Claims

### Claim 1

A microminiature thermionic converter comprising:
a first substrate comprising a dielectric material;
a second substrate comprising material selected from the group consisting of dielectric material and semiconductor material, the second substrate having a recess therein including at least one wall and a floor boundary, and the second substrate being positioned adjacent to the first substrate so that the recess opposes the first substrate:
a first conductor disposed in the first substrate and having a substantially flat surface bearing a first coating, the substantially flat surface bearing a first coating and facing the recess; and
a second conductor disposed in the second substrate and having a substantially flat surface bearing a second coating, the substantially flat surface bearing the second coating and extending from the floor boundary of the recess so that the surface of the first conductor and the surface of the second conductor are substantially parallel and opposite each other.

### Claim 2 (depends on 1)

The microminiature thermionic converter of claim 1 wherein the first coating has a first work function and is selected from the group consisting of BaO, SrO, CaO, Sc2O3 and a mixture of BaSrCaO, Sc2O3 and metal, and any combinations thereof, and the second coating is different from the first coating and has a second work function different from the first work function.

### Claim 3 (depends on 2)

The microminiature thermionic converter of claim 2 wherein the second coating is selected from the group consisting of BaO, SrO, CaO, Sc2O3, and a mixture of BaSrCaO, Sc2O3 and metal, and any combinations thereof.

### Claim 4 (depends on 3)

The microminiature thermionic converter of claim 3 wherein the first conductor and the second conductor are electrically connected via a device consuming electrical power.