# US 8,541,678 B2 · Thermionic/thermotunneling thermo-electrical converter

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- Number: US 8,541,678 B2
- Document ID: US8541678B2
- Status: Granted
- Kind: B2
- Application number: 11/992,995
- Filed: 2006-10-04
- Published: 2009-09-10
- Granted: 2013-09-24
- Earliest claimed: 2005-03-14
- Assignees: Borealis Technical Limited
- Applicants: Hans Juergen Walitzki; Isaiah Watas Cox
- Inventors: Hans Juergen Walitzki; Isaiah Watas Cox
- Web page: https://patentgrep.com/patent/US8541678B2

## CPC

- H10W 40/00: Arrangements for thermal protection or thermal control (integrated devices comprising arrangements for thermal protection H10D89/60)
- 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)}
- H10N 10/17: characterised by the structure or configuration of the cell or thermocouple forming the device
- H10W: GENERIC PACKAGES, INTERCONNECTIONS, CONNECTORS OR OTHER CONSTRUCTIONAL DETAILS OF DEVICES COVERED BY CLASS H10
- H01J: ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS (spark-gaps H01T; electric arc lamps H05B31/00; particle accelerators H05H)
- H10N: ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR

## Abstract

A thermionic or thermotunneling converter consisting of two electrodes maintained at a desired distance from one another by means of spacers in which the electrodes comprise silicon coated with a hard material, or comprise a ceramic or other refractory material. The spacers are formed by oxidizing one electrode, protecting certain oxidized areas and removing the remainder of the oxidized layer. The protected oxidized areas remain as spacers. These spacers have the effect of maintaining the electrodes at a desired distance without the need for active elements, thus greatly reducing costs.

## Claims

### Claim 1

A thermoelectric converter comprising:
a) a first wafer carrying a first array comprising a plurality of electrodes, said first array disposed horizontally;
b) a second wafer carrying a second array comprising a plurality of electrodes having surfaces substantially facing said electrodes of said first array;
c) a respective spacer or plurality of spacers disposed between said arrays to allow gaps of 10-15 nanometers between said electrodes, wherein the surface area of the spacer or plurality of spacers in direct contact with said surfaces is less than the surface area of said surfaces, and wherein said spacers comprise oxidized silicon.

### Claim 2 (depends on 1)

The converter of claim 1, wherein one or more of said electrodes comprises a silicon substrate.

### Claim 3 (depends on 2)

The converter of claim 2 wherein said silicon substrate includes a coating formed of a hard protective material.

### Claim 4 (depends on 3)

The converter of claim 3 wherein said coating of said hard protective material comprises a material that reduces the diffusivity of metals into silicon.

### Claim 5 (depends on 3)

The converter of claim 3 wherein said coating of said hard protective material comprises CVD diamond, Al2O3, Si3N4, or a metal.

### Claim 6 (depends on 1)

The converter of claim 1, wherein one or more of said electrodes includes a substrate comprising a material with a high melting temperature, thereby preventing said material from reacting with, diffusing into or flowing into adjacent regions.

### Claim 7 (depends on 6)

The converter of claim 6, wherein said substrate comprises a refractory material.

### Claim 8 (depends on 7)

The converter of claim 7 wherein said refractory material comprises a ceramic.

### Claim 9 (depends on 6)

The converter of claim 6, wherein said substrate includes a coating formed from a thin film comprising an amorphous or poly-crystalline silicon.

### Claim 10 (depends on 1)

The converter of claim 1, wherein a surface of one or more of said plurality of electrodes has a periodically repeating structure which creates de Broglie wave interference.

### Claim 11 (depends on 10)

The converter of claim 10 wherein said periodically repeating structure comprises one or more indents of a depth less than approximately 50 nm and a width less than approximately 1 μm, whereby deBroglie interference is created and work function of said plurality of electrodes is reduced.

### Claim 12 (depends on 1)

The converter of claim 1, wherein said spacers further comprise a protective layer.

### Claim 13 (depends on 1)

The converter of claim 1, wherein said first array comprises a hot side and said second array comprises a cold side.

### Claim 14 (depends on 1)

The converter of claim 1, wherein said first array comprises a cold side and said second array comprises a hot side.

### Claim 15 (depends on 1)

The converter of claim 1, wherein said first wafer carrying said first array of said plurality of electrodes comprises a silicon substrate with a thin surface film of oxidized silicon, and wherein said electrodes include exposed areas of silicon where said oxidized silicon has been removed and areas where said oxidized silicon has not been removed comprising said spacers.

### Claim 16 (depends on 15)

The converter of claim 15, wherein said spacers include a protective layer on said oxidized silicon.

### Claim 17 (depends on 15)

The converter of claim 15, wherein said exposed areas of said electrodes have a surface layer comprising a material structured to have a work function of 1 eV or less.

### Claim 18 (depends on 1)

The converter of claim 1, wherein said electrodes are rectangular and said spacers comprise a plurality of dots arranged on said rectangular electrodes.

### Claim 19

A method for building a thermoelectric converter comprising the steps of:
a) providing a first wafer carrying a first array comprising a plurality of electrodes and disposing said first array horizontally;
b) providing a second wafer carrying a second array comprising a plurality of electrodes having surfaces substantially facing said electrodes of said first array;
c) forming a respective spacer or plurality of spacers disposed between said first and second arrays to create gaps of 10-15 nanometers between said electrodes by oxidizing said electrodes, protecting selected areas of said oxidized electrodes, and removing areas of said oxidized electrodes which have not been protected, whereby said protected areas remain as protrusions comprising said spacers, wherein the selected protected areas represent a minority of said oxidized electrodes and the surface area of the spacer or plurality of spacers in direct contact with said electrode surfaces is less than the surface area of said electrode surfaces; and
d) connecting said electrodes of said first array to a said electrodes of said second array, whereby said electrodes are positioned substantially facing each other, with a gap of 10-15 nanometers between them maintained by said protrusions.

### Claim 20 (depends on 19)

The method of claim 19 wherein said step of protecting selected areas of said oxidized surface comprises forming dots by means of photolithographic processes.

### Claim 21 (depends on 19)

The method of claim 19 wherein said step of removing unprotected areas of said oxidized surface comprises etching.

### Claim 22 (depends on 19)

The method of claim 19 additionally comprising the step of: introducing a layer of a material having a work function of 1 eV or less onto a surface of said first electrode array.

### Claim 23 (depends on 19)

The method of claim 19 wherein said step of connecting said first electrode array to said second electrode array is performed in a vacuum chamber.

### Claim 24 (depends on 19)

The method of claim 19 wherein said step of connecting said first electrode array to said second electrode array is performed in a chamber filled with a controlled gas atmosphere which reacts with the electrode material and forms a vacuum between the electrodes.

### Claim 25 (depends on 19)

The method of claim 19, further comprising bonding a wafer with said spacers to a completely processed sheet of silicon carrying a multitude of integrated circuits by:
a) thinning said sheet of integrated circuits to a thickness of 50-200 μm by grinding or etching the sheet from its back side,
b) polishing the back side of said sheet of integrated circuits to obtain a surface roughness of 1-20 Å to obtain conditions for direct bonding,
c) optionally adding a surface film or structure to lower the work function of the integrated circuit wafer back side,
d) bonding said sheet of integrated circuits to a second wafer containing spacers at temperatures not higher than the maximum temperature the integrated circuit wafer can withstand, and
e) dicing the composite wafer to form individual integrated circuits with integrated active cooling.

### Claim 26 (depends on 25)

The method of claim 25 wherein said wafer comprises a silicon wafer bonded to a wafer with an array of electrodes that has said spacers comprising of:
a) bonding said wafers to form a composite wafer, and
b) dicing said composite wafer to obtain individual diodes.

### Claim 27 (depends on 26)

The method of claim 26 wherein said individual diodes are mounted to a conventional heat sink to which standard, packaged integrated circuits are mounted.

### Claim 28 (depends on 26)

The method of claim 26 wherein said individual diodes are mounted on an enclosure wherein said enclosure is suitable for power generation.

### Claim 29 (depends on 25)

The method of claim 25, wherein the back side of said sheet of integrated circuits is polished to obtain a surface roughness of less than 5 Å.

### Claim 30 (depends on 19)

The method of claim 19, wherein said first or said second array comprises silicon and a hard protective material is coated on said silicon.

### Claim 31 (depends on 30)

The method of claim 30, wherein said hard protective material is physically or chemically introduced to said silicon to coat said silicon.

### Claim 32 (depends on 19)

The method of claim 19, wherein said first or second array further comprises a substrate, wherein said substrate is coated with a thin film coating of amorphous or poly-crystalline silicon and said thin film is smoothened by chemical-mechanical polishing or etching techniques.

### Claim 33 (depends on 19)

The method of claim 19, wherein said spacers are formed in the same place on each of said electrodes, wherein when said first array of electrodes and said second array of electrodes are connected, said spacers on both arrays meet and create said gaps between said electrodes with a distance equal to twice the height of each said spacer.