# US 5,705,318 A · Micromotors and methods of fabrication

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- Number: US 5,705,318 A
- Document ID: US5705318A
- Status: Granted
- Kind: A
- Application number: 08/254,920
- Filed: 1994-06-06
- Granted: 1998-01-06
- Earliest claimed: 1994-06-06
- Assignees: Case Western Reserve University
- Inventors: Mehran Mehregany; Keren Deng
- Web page: https://patentgrep.com/patent/US5705318A

## CPC

- B81C 1/00198: {comprising elements which are movable in relation to each other, e.g. comprising slidable or rotatable elements}
- G02B 26/0816: {by means of one or more reflecting elements}
- G02B 26/106: {having diffraction gratings as scanning elements, e.g. holographic scanners (holographic optical elements G02B5/32, holography G03H)}
- H02N 1/004: {in which a body is moved along a path due to interaction with an electric field travelling along the path}
- B81B 2201/034: Electrical rotating micromachines
- B81C: PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS (making microcapsules or microballoons B01J13/02; processes or apparatus specially adapted for the manufacture or treatment of piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/01)
- G02B: OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- H02N: ELECTRIC MACHINES NOT OTHERWISE PROVIDED FOR
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)

## Abstract

A polysilicon micromotor, of either inner rotor or outer rotor design, is fabricated with a process that uses as few as three mask steps. In an outer rotor (wobble) micromotor, a free-rotating insulating flange bearing mechanically couples the inner periphery of the rotor to the stator, permitting the outer periphery of the rotor to be directly coupled to other mechanisms. The dielectric constant of the flange bearing increases motive torque of the motor as contrasted with air-gap designs. This and other factors results in motive torque, in the illustrated embodiment, more than 100 times larger than in previous designs. Among its other benefits, the disclosed fabrication process results in in-place formation of all motor elements, and enables precise definition of the rotor/stator gap.

## Claims

### Claim 1

In a process of fabricating an outer rotor micromotor having a rotor and a stator on a substrate, the rotor not overlapping the stator, an improvement comprising:
fabricating the rotor in place; and
defining a radial rotor/stator gap of less than 3.0 microns.

### Claim 2 (depends on 1)

The process of claim 1 which further includes integrating electronic circuitry for use with the micromotor on the same substrate as the micromotor.

### Claim 3 (depends on 1)

An outer rotor micromotor fabricated according to claim 1.

### Claim 4 (depends on 3)

The micromotor of claim 3 which further includes an electrically insulating member having a dielectric constant greater than two disposed in said gap.

### Claim 5 (depends on 4)

The micromotor of claim 4 in which the electrically insulating member is a flange bearing that serves to mechanically couple the rotor and stator.

### Claim 6 (depends on 4)

The micromotor of claim 4 in which the electrically insulating member is not affixed to either the stator nor to the rotor, nor to said substrate.

### Claim 7 (depends on 3)

A mechanical system including a plurality of micromotors according to claim 3.

### Claim 8 (depends on 1)

The method of claim 1 which includes fabricating said rotor of polysilicon.

### Claim 9

In a process of fabricating a micromotor on a substrate by a series of photolithographic steps, the micromotor having a rotor held in place by a flange, and a stator, an improvement wherein:
a gap between the rotor and stator is defined in a first of said photolithographic steps;
the flange is disposed between the rotor and stator and has a dielectric constant greater than two; and
said flange is not affixed to either the stator nor to the rotor, nor to said substrate.

### Claim 10 (depends on 9)

The method of claim 9 in which said flange has a dielectric constant of more than 500.