Patent Application
20080157354
This invention relates to fabrication of vertically stacked, multiple nanostructure arrays, and to very small control devices, and specifically to control devices which incorporate a variety of nanostructures.
A number of different materials have been investigated as components of nanostructure devices. The materials include semiconductors, metals, oxides, compounds, and even polymers. High aspect ratio single crystalline IrO2 nanowires and TiO2 nanorods array have been fabricated, as previously disclosed in U.S. patent application Ser. No. 11/582,197, filed Oct. 16, 2006, for Solar Cell Structures using Porous Column TiO2 Films deposited by CVD, and U.S. Patent Publication No. 2006/0086314-A1, published Apr. 27, 2006, for Iridium Oxide Nanowires and Method for Forming Same, which are incorporated herein by reference. The single crystal IrO2 nanowire is conductive and may be used as an electrode, while TiO2 nanorods have applications in sensors and solar cells.
Although different materials have been explored, known works are limited to use of a single type of nanostructure, using a single type of material. There is no known report on the use of multiple materials or on stacked nanostructures, wherein the stacked nanostructures are of different structural types.
A method of fabricating a stacked nanostructure array includes preparing a substrate; forming a bottom electrode directly on the substrate; growing a first nanostructure array directly on the bottom electrode; forming an insulating layer on the first nanostructure array; exposing the upper surface of the first nanostructure array; depositing a second, and subsequent, nanostructure array on a nanostructure array immediately below the second and subsequent nanostructure array; repeating said forming, said exposing and said depositing a subsequent steps to form a stacked nanostructure array; removing an uppermost insulating layer; and forming a top electrode on an uppermost nanostructure array. A sensor incorporating the nanostructure array includes top and bottom electrodes with plural layers of nanostructure array therebetween.
It is an object of the invention to provide a stacked array of nanostructures.
Another object of the invention is to fabricate a stacked array of nanostructures having different base material therein.
A further object of the invention is to fabricate a stacked array of nanostructures having different nanostructure components.
This summary and objectives of the invention are provided to enable quick comprehension of the nature of the invention. A more thorough understanding of the invention may be obtained by reference to the following detailed description of the preferred embodiment of the invention in connection with the drawings.
A vertical stacked, multiple nanostructure array is disclosed as an example of the method of the invention hereof. A stacked nanostructure fabricated according to the method of the invention has applications as an efficient and cost effective control device, and in environment controls, energy generation, energy storage, and various types of sensors.
The method of the invention provides a technique for fabricating a device wherein a nanostructured material is stacked on top of the another nanostructured material, while still maintaining vertical continuity and lateral porous structure of the entire stack.
Referring now to
In order to prevent the next nanostructure array material from being deposited into the pores present in the bottom nanostructure array, an insulating layer is formed 18, which may be silicon-on-glass (SOG), and which may be formed by spin coating onto the bottom nanostructure array. A curing process, subsequent etching or CMP process, is performed 20 to expose the tips of the bottom nanostructure array layer.
An optional seed layer may be deposited 22 prior to subsequent nanostructure array formation. The purpose of the seed layer is to promote nanostructure array formation on any lower nanostructure array and to maintain the continuity of the stacked nanostructure arrays.
A nanostructure array is deposited 24 on the first nanostructure array, and the next insulating layer is then deposited, as in step 18. This process continues through steps 20, 22 until all the nanostructure layers have been deposited.
After all the nanostructure arrays are deposited, the uppermost insulating layer may be removed 26, as by selective etching, leaving the stand-alone, multiple stacked nanostructure array. A top electrode is formed on the uppermost nanostructure layer 28. A stacked nanowire array fabricated according to the method of the invention is depicted in
The process conditions to grow TiO2 nanorods array is the same as disclosed in U.S. patent application Ser. No. 10/971,330, filed Oct. 24, 2004, for Iridium Oxide Nanowires and Method for Forming Same. After TiO2 nanorod array formation, the wafer is placed in a growth chamber for IrO2 nanowire formation. The condition to grow IrO2 nanowires is the same as disclosed in U.S. patent application Ser. No. 11/582,197, filed Oct. 16, 2006, for Solar Cell Structures using Porous Column TiO2 Films deposited by CVD.
Nanomaterials which may be stacked on top of each other may be of different nanostructure forms, such as nanowires, nanotubes, nanorods, nanoparticles, nanobelts, nanocombs, 3D nanostructures, etc. The nanostructures may also be of different densities in the array and have different diameters. The nanomaterial include, but not limited to, TiO2, ZnO, SnO2, Sb2O3, In2O3, WO3, and carbon. Additionally, carbon nanotubes, metal nanowires, such as Pd, Pt, Au, Mo, and semiconductor nanowires such as Si, Ge, SiGe, CdSe, AlN, ZnS, GaN, InP, InAs, PbSe, PbS, and IrO2, etc., may be stacked in the stacked nanostructure array fabricated according to the method of the invention.
This vertical stacked nanowires arrays structure may be used for environment control, energy generation, energy storage and sensor applications. A gas sensor application is described in U.S. patent application Ser. No. 11/264,113, filed Nov. 1, 2005, for Ambient Environment Nanowire Sensor, incorporated herein by reference, which uses an IC compatible process to fabricate nanowire array sensor structure. The structure includes a single stack nanowire array that may be coated with different materials for different sensing capabilities. In this invention, the single nanowire array is replaced by multiple stacked nanowire arrays. After all the nanowires arrays have been deposited, and the SOG has been deposited, the very top layer of the SOG is removed, by etching or CMP, to expose the tips of the top nanowire array. The top electrode is deposited and a stack etching is performed. After the stack etching, a selective etching of the SOG is performed to expose the outer rim of the stacked nanowire arrays. The center region of SOG is left, in situ, to support the structure. These procedures are similar to the process that has been disclosed in the above-identified pending application for a single nanostructure array.
Because the exposed outer rim of the nanostructure stack has different sensing materials exposed to the ambient atmosphere, each of the nanomaterials sense a different gas(es), resulting in a much broader sensing spectrum for the sensor.
Stacked nanostructure arrays are depicted in
Thus, a method to from a stacked nanostructure device has been disclosed. It will be appreciated that further variations and modifications thereof may be made within the scope of the invention as defined in the appended claims.
