Aluminum doped zinc oxide deposited by atomic layer deposition and its applications to micro/nano devices

Abstract

This work reports investigation on the deposition and evaluation of an aluminum-doped zinc oxide (AZO) thin film and its novel applications to micro- and nano-devices. The AZO thin film is deposited successfully by atomic layer deposition (ALD). 50 nm-thick AZO film with high uniformity is checked by scanning electron microscopy. The element composition of the deposited film with various aluminum dopant concentration is analyzed by energy-dispersive X-ray spectroscopy. In addition, a polycrystalline feature of the deposited film is confirmed by selected area electron diffraction and high-resolution transmission electron microscopy. The lowest sheet resistance of the deposited AZO film is found at 0.7 kΩ/□ with the aluminum dopant concentration at 5 at.%. A novel method employed the ALD in combination with the sacrificial silicon structures is proposed which opens the way to create the ultra-high aspect ratio AZO structures. Moreover, based on this finding, three kinds of micro- and nano-devices employing the deposited AZO thin film have been proposed and demonstrated. Firstly, nanowalled micro-hollows with an aspect ratio of 300 and a height of 15 µm are successfully produced . Secondly, micro- and nano-fluidics, including a hollow fluidic channel with a nanowall structure as a resonator and a fluidic capillary window as an optical modulator is proposed and demonstrated. Lastly, nanomechanical resonators consisting of a bridged nanobeam structure and a vertical nanomechanical capacitive resonator are fabricated and evaluated.

Investigation on Transparent, Conductive ZnO:Al Films Deposited by Atomic Layer Deposition Process

“…In order to observe microstructure and film thickness simultaneously, the cycle number of the ZnO and AZO film were scaled down to 150. As shown in Figure 5 a,b, both the ZnO and AZO film exhibit a polycrystalline lattice structure, which is consistent with previously-reported works [ 34 , 35 ]. Noticeably, the thickness of the AZO film (18 nm) is thinner than that of the ZnO film (20 nm).…”

Growth of Aluminum Doped Zinc Oxide Nanostructure Thin Films by Nonconventional Sol‐Gel Method

“…This result is similar to other reported results with AZO thin films grown by other methods. [8,13,19,21,23,29,31,32,35,36,[39][40][41][42]44,[47][48][49][50][51][52][53][54][55][56][57][58] The Hall measurement results are listed in Table 4; from this table, it can be found that the higher value of conductivity and carrier concentration were achieved at 3 wt% doping concentrations as shown in Figure 8…”

“…[7,11,12,13,[15][16][17]19,28,30,[32][33][34][38][39][40][41][42][43][44][45][46][47][48][49][50][51] The conductivity and carrier concentration increased with increasing the aluminum, which is similar to other reported results by other methods. [8,13,19,21,23,29,31,32,35,36,[39][40][41][42]44,[47][48][49][50][51][52][53][54][55][56]…”

“…This material is one of most suitable materials, so it has been studied widely in the recent decade because of its special physical, chemical properties such as direct band gap energy, large exciton binding energy (60 meV) at room temperature, good crystalline quality, high optical transparency, wide band gap at room temperature (3.3 eV), strong room temperature luminescence, good electrical DOI: 10.1002/masy.202100350 conductivity, piezoelectricity, chemical stability, thermal stability, abundance in nature and nontoxicity, etc. [1][2][3][4][5][6][7][8] These features make ZnO thin films very attractive for different applications like transparent conductor oxide, gas sensors, piezoelectric sensors, semiconductor heterojunctions, solar cells, surface acoustic wave devices, light emitting diodes, nanolasers, and electrophotography. [4,[8][9][10][11][12][13] The undoped zinc oxide films having n-type conductivity, the transparency, band gap, and conductivity can be increased by adding dopants from to the II and III group such as Al, In,Ga, Cu, and Cd, [6,9,10,14,15] among these elements, Al is as of the most effective donor dopants because it is cheap, abundant, non-toxic material, and easy incorporation into the ZnO crystal structure.…”

“…[1][2][3][4][5][6][7][8] These features make ZnO thin films very attractive for different applications like transparent conductor oxide, gas sensors, piezoelectric sensors, semiconductor heterojunctions, solar cells, surface acoustic wave devices, light emitting diodes, nanolasers, and electrophotography. [4,[8][9][10][11][12][13] The undoped zinc oxide films having n-type conductivity, the transparency, band gap, and conductivity can be increased by adding dopants from to the II and III group such as Al, In,Ga, Cu, and Cd, [6,9,10,14,15] among these elements, Al is as of the most effective donor dopants because it is cheap, abundant, non-toxic material, and easy incorporation into the ZnO crystal structure. [9,16,17] Furthermore, the addition of aluminum ions to zinc sol solution can increase the number of nucleation sites.…”