Bioresorbable Silicon Electronics for Transient Implants

Patent metadata

Field	Value
Publication number	US-2017128015-A1
Application number	US-201615349525-A
Country	US
Kind code	A1
Filing date	Nov 11, 2016
Priority date	Nov 11, 2015
Publication date	May 11, 2017
Grant date	—

Abstract

Provided are implantable and bioresorbable medical devices comprising a bioresorbable substrate and an electronic circuit supported by the bioresorbable substrate. The electronic circuit comprises a membrane of silicon having a thickness less than or equal to 5 μm and an array of dissolvable electrodes, wherein the dissolvable electrodes are formed from the membrane of silicon. The electronic circuit is configured to conformally contact a biological tissue and electrically interface with biological tissue during use. The silicon may be highly doped to provide the requisite characteristics for electrically interfacing with biological tissue, and may be further used to form other components of the electronic circuit, including back-plane transistors electrically connected to the electrode array.

First claim

We claim:

1 . An implantable and bioresorbable medical device comprising:
a bioresorbable substrate; an electronic circuit supported by said bioresorbable substrate, wherein said electronic circuit comprises a membrane of silicon having a thickness less than or equal to 5 μm; an array of dissolvable electrodes, wherein said dissolvable electrodes are formed from said membrane of silicon; and wherein said electronic circuit is configured to conformally contact a biological tissue and electrically interface with biological tissue during use.

2 . The device of claim 1 , wherein said dissolvable electrodes are configured to undergo hydrolysis upon contact with a biofluid.

3 . The device of claim 1 , wherein said array of dissolvable electrodes are a multiplexed array of dissolvable electrodes.

4 . The device of claim 3 , further comprising an array of backplane transistors formed from said membrane of silicon in electrical contact with said array of dissolvable electrodes for high speed multiplexed addressing of said array of dissolvable electrodes.

5 . The device of claim 4 , wherein said transistors are MOSFETs.

6 . The device of claim 5 , wherein said MOSFETs comprise a thin film of a metal, a gate dielectric and an interlayer dielectric.

7 . The device of claim 6 , wherein:
said metal comprises Mo having a thickness less than 500 nm; said gate dielectric comprises SiO 2 having a thickness less than 200 nm; said interlayer dielectric comprises a multilayer stack of SiO 2 with a thickness less than 400 nm, Si 3 N 4 with a thickness less than 500 nm, and SiO 2 with a thickness less than 400 nm.

8 . The device of claim 4 , further comprising for each electrode:
a buffer transistor electrically connected to said electrode for buffering of a measured tissue potential; and a multiplexing transistor electrically connected to said electrode for multiplexing of said array of electrodes.

9 . The device of claim 8 , further comprising a second thin layer of metal to define column select lines.

10 . The device of claim 1 , wherein said membrane of silicon is patterned to form a plurality of parallel silicon ribbons, the device further comprising:
an encapsulation layer that covers a portion of said plurality of parallel silicon ribbons; and a plurality of passages formed through said encapsulation layer, wherein the passages are aligned with said parallel silicon ribbons to form an array of exposed silicon electrically interconnected to regions of encapsulated silicon ribbons.

11 . The device of claim 10 , further comprising a plurality MOSFETs formed from said membrane of silicon, wherein said membrane of silicon serves as both an active semiconductor material and a tissue interface electrode.

12 . The device of claim 10 , further comprising an active region at a distal end of said parallel silicon ribbons connected to external electrical connectors separated from said distal end by a longitudinal distance that is greater than or equal to 3 mm.

13 . The device of claim 4 , further comprising vertical interconnects to electrically connect said electrodes to said backplane transistors, and said electrodes are configured for physical contact with underlying tissue.

14 . The device of claim 13 , wherein said vertical interconnects comprise vias.

15 . The device of claim 4 , further comprising an encapsulation layer that covers said backplane transistors and said membrane of silicon.

16 . The device of claim 15 , wherein said encapsulation layer comprises a trilayer of SiO 2 /Si 3 N 4 /SiO 2 .

17 . The device of claim 16 , wherein said encapsulation layer has a thickness less than or equal to 2 μm.

18 . The device of claim 15 , further comprising a plurality of passages through said encapsulation layer and in spatial alignment with an active region of each of said electrodes.

19 . The device of claim 1 , configured for accurate measurement of a biological parameter over a device lifetime.

20 . The device of claim 19 , wherein the device lifetime is for a chronic monitoring application that is greater than or equal to 10 days.

21 . The device of claim 19 , wherein the device lifetime is for an acute monitoring application that is less than or equal to 2 days.

22 . The device of claim 19 , wherein said membrane of silicon has a thickness that decreases as a function of implant duration, wherein said device maintains functionality for a decrease in thickness of up to 70%.

23 . The device of claim 19 , wherein device lifetime is increased with increasing dopant concentration and/or increasing silicon membrane thickness.

24 . The device of claim 1 , wherein said membrane of silicon is doped with a high concentration of dopant.

25 . The device of claim 24 , wherein said high concentration is greater than or equal to 10 18 cm −3 and less than or equal to 2×10 20 cm −3 .

26 . The device of claim 24 , wherein said dopant is selected from the group consisting of phosphorus and boron.

27 . The device of claim 1 , further comprising an insulation layer and electrical interconnects that electrically connect said electrodes, wherein said insulation layer electrically isolates interconnects from biofluids and biological tissue during use.

28 . The device of claim 27 , wherein the insulation layer comprises a layer of SiO 2 having a thickness less than or equal to 200 nm.

29 . The device of claim 1 , wherein said membrane of silicon further comprises terminal pads configured to electrically interface with a biological tissue.

30 . The device of claim 29 , wherein said terminal pads are exposed Si of said membrane of Si.

31 . The device of claim 1 , wherein bioresorption comprises controlled dissolution of said membrane of Si

32 . The device of claim 31 , wherein said controlled dissolution is characterized by one or more of no observable: cracks, flakes, particulates, or decrease in surface smoothness.

33 . The device of claim 31 , wherein said controlled dissolution has an average dissolution rate characterized by a decrease in Si membrane thickness that is greater than or equal to 5 nm/day and less than or equal to 15 nm/day.

34 . The device of claim 31 , having a dissolution rate for other non-Si membrane components of the device, including an insulating layer or said bioresorbable substrate, that is between 3 nm/day and 12 nm/day.

35 . The device of claim 1 , having one or more material parameters selected to obtain a desired dissolution time of said device, the material parameters including one or more of silicon membrane thickness, silicon membrane doping level, or composition of polymer substrate.

36 . The device of claim 1 , wherein during use there is no detectable long-term adverse immune response.

37 . The device of claim 1 , capable of being bent from a planar configuration to a curved configuration with a radius of curvature up to 3 mm without adverse degradation of device functionality.

38 . The device of claim 1 for spatio-temporal mapping of electrical activity for a biological tissue.

39 . The device of claim 38 , wherein said biological tissue is a cerebra

Assignees

• Univ Illinois

Inventors

• Rogers John A
• Yu Ki Jun

Classifications

• A61B2562/0209

  Special features of electrodes classified in A61B5/24, A61B5/25, A61B5/283, A61B5/291, A61B5/296, A61B5/053 · CPC title

• A61B5/6868 Primary

  Brain · CPC title

• A61L31/028

  Other inorganic materials not covered by A61L31/022 - A61L31/026 · CPC title

• A61L31/148

  Materials at least partially resorbable by the body · CPC title

• A61B2562/046

  in a matrix array · CPC title