Microfabricated gas flow structure

Patent metadata

Field	Value
Publication number	US-2016230751-A1
Application number	US-201615006034-A
Country	US
Kind code	A1
Filing date	Jan 25, 2016
Priority date	Jan 25, 2015
Publication date	Aug 11, 2016
Grant date	—

Abstract

A microfabricated gas flow structure includes an array of vertical gas flow channels in a side-by-side parallel flow arrangement. Adjacent gas flow channels are separated by a thin wall having a thickness which can be an order of magnitude or more less than the channel width, offering exceptionally high area efficiency for the array. Channel walls can be formed from a dielectric material to provide the walls with sufficient integrity at nanoscale thicknesses and to provide thermal insulative properties in the lateral direction, thereby controlling power losses when the gas flow structure is employed as a Knudsen pump. The gas flow structure can be microfabricated as a monolithic structure from an SOI wafer, with the gas flow channels formed in the device layer and the heat sink formed from the handle layer.

First claim

1 . A method of microfabricating a gas flow structure, the method comprising the steps of:
(a) providing a substrate having a planar surface; (b) forming an array of gas flow channels into the substrate, each gas flow channel extending between an inlet end and an outlet end in a direction normal to the planar surface, wherein adjacent gas flow channels of the array are separated by a layer of dielectric material; (c) forming a first support layer from the substrate at the inlet end of the channels; and (d) forming a second support layer at the outlet end of the gas flow channels so that the array of gas flow channels is supported between the first and second support layers.

2 . The method of claim 1 , further comprising the step of forming a heat source supported by the second support layer at the outlet end of the gas flow channels, wherein the first support layer is formed as a heat sink.

3 . The method of claim 1 , wherein the substrate is a multi-layer wafer comprising a device layer and a handle layer separated by a dielectric layer, the gas flow channels being formed in the device layer.

4 . The method of claim 1 , wherein the substrate is a multi-layer wafer comprising a device layer and a handle layer separated by a dielectric layer, the first support layer being formed from the handle layer.

5 . The method of claim 1 , wherein the gas flow channels are formed in a device layer of a silicon-on-insulator (SOI) wafer, and the first support layer is formed from a handle layer of the SOI wafer.

6 . The method of claim 1 , wherein step (b) comprises the steps of:
(i) forming an array of trenches into the substrate surface, each trench having opposing walls connected by a bottom wall; (ii) coating the opposing walls of each trench with the dielectric material; and (iii) removing at least a portion of the bottom wall of each coated trench to form the inlet end of the gas flow channels.

7 . The method of claim 6 , wherein step (ii) is performed by atomic layer deposition.

8 . The method of claim 6 , further comprising the steps of:
filling each coated trench with an etchable material before step (iii); forming one or more heat sink channels into the substrate from a side of the substrate opposite the planar surface, wherein the step of forming the one or more heat sink channels includes step (iii) so that the etchable material is exposed in the formed heat sink channels; coating walls of the formed heat sink channels with a dielectric material; and etching the etchable material from between the opposing walls of each coated trench, wherein the dielectric material from the step of coating walls of the formed heat sink channels prevents the first support layer from being etched.

9 . The method of claim 8 , wherein the step of coating walls of the formed heat sink channels comprises atomic layer deposition of Al 2 O 3 on opposing walls and a bottom wall of each heat sink channel, the method further comprising reactive ion etching of each heat sink channel, whereby the Al 2 O 3 is removed from the bottom wall of each heat sink channel but not from the opposing walls of each heat sink channel.

10 . The method of claim 1 , wherein the dielectric material is Al 2 O 3 .

11 . A microfabricated gas flow structure, comprising:
a first support layer at a inlet side of the structure, the first support layer comprising a plurality of gas inlet openings formed therethrough; a second support layer at an outlet side of the structure, the second support layer comprising a plurality of gas outlet openings formed therethrough; and an array of gas flow channels located between and fluidly connecting the gas inlet openings with the gas outlet openings, the gas flow channels of the array being in a parallel flow arrangement and each gas flow channel of the array being separated from an adjacent gas flow channel of the array by a wall, wherein each wall extends between an inlet end at the first support layer and an outlet end at the second support layer, and each gas flow channel of the array is sized for flow in the non-viscous flow regime in a flow direction between the inlet side and the outlet side of the structure.

12 . A microfabricated gas flow structure as defined in claim 11 , further comprising a heat source supported by the second support layer at the outlet side of the structure, the heat source being operable to induce gas flow through the array of gas flow channels whereby the microfabricated gas flow structure is a Knudsen pump.

13 . A microfabricated gas flow structure as defined in claim 12 , wherein the heat source is a thin film resistive heater comprising resistive portions located between adjacent gas outlet openings.

14 . A gas micropump comprising a Knudsen pump as defined in claim 12 stacked together with a second gas pump in a serial flow arrangement.

15 . A gas micropump comprising two or more Knudsen pumps as defined in claim 12 stacked together in a serial flow arrangement.

16 . A microfabricated gas flow structure as defined in claim 11 , wherein the thickness of each wall is at least an order of magnitude less than the distance between opposite walls of the same gas flow channel.

17 . A microfabricated gas flow structure as defined in claim 11 , further comprising:
an active pumping area, wherein the gas outlet openings are located entirely within the active pumping area; a thermal isolation zone circumscribing the active pumping area, wherein the array of gas flow channels lies entirely within the thermal isolation zone; and an outer rim area circumscribing the thermal isolation zone.

18 . A microfabricated gas flow structure as defined in claim 17 , wherein the array of gas flow channels occupies the entire thermal isolation zone such that gas flow channels at an outer portion of the array are at least partially blocked by the second support layer in the thermal isolation zone.

19 . A microfabricated gas flow structure as defined in claim 17 , wherein at least 20% of the active pumping area is open area not occupied by the second support layer or walls between adjacent gas flow channels.

20 . A microfabricated gas flow structure as defined in claim 11 , wherein the array of gas flow channels has a cross-sectional area, and 10% or less of the cross-sectional area is occupied by walls between adjacent gas flow channels.

21 . A microfabricated gas flow structure as defined in claim 20 , wherein 1% or less of the cross-sectional area is occupied by walls between adjacent gas flow channels.

22 . A microfabricated gas flow structure as defined in claim 11 , wherein each wall is fabricated from Al 2 O 3 .

Assignees

• Univ Michigan Regents

Inventors

• Gianchandani Yogesh
• An Seungdo
• Qin Yutao

Classifications

• B81C1/00063

  Trenches · CPC title

• B81C1/00071

  Channels · CPC title

• F04B19/006

  Micropumps (F04B43/043 and F04B43/095 take precedence) · CPC title

• F04B37/06 Primary

  for evacuating by thermal means · CPC title

• F04B19/24

  Pumping by heat expansion of pumped fluid · CPC title