Epitaxial Nanostructured α-Quartz Films on Silicon: From the Material to New Devices

Summary

This work presents a detailed protocol for the microfabrication of nanostructured α-quartz cantilever on a Silicon-On-Insulator(SOI) technology substrate starting from the epitaxial growth of quartz film with the dip coating method and then nanostructuration of the thin film via nanoimprint lithography.

Abstract

In this work, we show a detailed engineering route of the first piezoelectric nanostructured epitaxial quartz-based microcantilever. We will explain all the steps in the process starting from the material to the device fabrication. The epitaxial growth of α-quartz film on SOI (100) substrate starts with the preparation of a strontium doped silica sol-gel and continues with the deposition of this gel into the SOI substrate in a thin film form using the dip-coating technique under atmospheric conditions at room temperature. Before crystallization of the gel film, nanostructuration is performed onto the film surface by nanoimprint lithography (NIL). Epitaxial film growth is reached at 1000 °C, inducing a perfect crystallization of the patterned gel film. Fabrication of quartz crystal cantilever devices is a four-step process based on microfabrication techniques. The process starts with shaping the quartz surface, and then metal deposition for electrodes follows it. After removing the silicone, the cantilever is released from SOI substrate eliminating SiO₂ between silicon and quartz. The device performance is analyzed by non-contact laser vibrometer (LDV) and atomic force microscopy (AFM). Among the different cantilever’s dimensions included in the fabricated chip, the nanostructured cantilever analyzed in this work exhibited a dimension of 40 µm large and 100 µm long and was fabricated with a 600 nm thick patterned quartz layer (nanopillar diameter and separation distance of 400 nm and 1 µm, respectively) epitaxially grown on a 2 µm thick Si device layer. The measured resonance frequency was 267 kHz and the estimated quality factor, Q, of the whole mechanical structure was Q ~ 398 under low vacuum conditions. We observed the voltage-dependent linear displacement of cantilever with both techniques (i.e., AFM contact measurement and LDV). Therefore, proving that these devices can be activated through the indirect piezoelectric effect.

Introduction

Oxide nanomaterials with piezoelectric properties are pivotal to design devices such as MEMS sensors or micro energy harvesters or storage^1,2,3. As the advances in CMOS technology increase, the monolithic integration of high-quality epitaxial piezoelectric films and nanostructures into silicon becomes a subject of interest to expand new novel devices⁴. In addition, greater control of miniaturization of these devices is required to achieve high performances^5,6. New sensor applications in electro....

Protocol

1. Preparation of the solution

1. Prepare a solution containing prehydrolyzed tetraethyl orthosilicate (TEOS) 18 h before the production of the gel films in a fume hood in which a lab balance and a magnetic stirrer are placed.
   1. Add 0.7 g of polyethylene glycol hexadecyl ether (Brij-58) and 23.26 g of ethanol into 50 mL bottle and close the lid of the bottle and stir it until the Brij is completely dissolved.
   2. Add 1.5 g of HCl 35% into the flask in step 1.1.1, close it and stir for 20 s.
   3. Add 4.22 g of TEOS to the flask in step 1.1.2, close it and let it stir for 18 h.
2. Preparation of 1 M aqueous solution o....

Results

The progress of the material synthesis and device fabrication (see Figure 1) was depicted schematically by monitoring different steps with real images. After the microfabrication processes, we observed the aspect of the nanostructured cantilevers using the field emission Scanning Electron Microscopy (FEG-SEM) images (Figure 2a-c). 2D Micro X-ray diffraction controlled the crystallinity of the different stacking layers of the cantilever (

Discussion

The presented method is a combination of bottom-up and top-down approaches to produce nanostructured piezoelectric quartz micro-cantilevers on Si. Quartz/Si-MEMS technology offers major advantages over bulk quartz in terms of size, power consumption, and integration cost. Indeed, epitaxial quartz/Si MEMS are produced with CMOS-compatible processes. This could facilitate the future fabrication of single chip solutions for multifrequency devices while preserving miniaturization and cost-effective processes. Compared to the.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Acetone	Honeywell Riedel de Haën	UN 1090
AZnLOF 2020 negative resist	Microchemicals	USAW176488-1BLO
AZnLOF 2070 negative resist	Microchemicals	USAW211327-1FK6
AZ 726 MIF developer	Merck	DEAA195539
BOE (7:1)	Technic	AF 87.5-12.5
Brij-58	Sigma	9004-95-9
Chromium	Neyco	FCRID1T00004N-F53-062317/FC79271
Dip Coater ND-R 11/2 F	Nadetec	ND-R 11/2 F
Hydrogen peroxide solution 30%	Carlo Erka Reagents DasitGroup	UN 2014
H2SO4	Honeywell Fluka	UN 1830
Isopropyl alcohol	Honeywell Riedel de Haën	UN 1219
Mask aligner	EV Group	EVG620
PG remover	MicroChem	18111026
Platinum	Neyco	INO272308/F14508
PTFE based container	Teflon
Reactive ion etching (RIE)	Corial	ICP Corial 200 IL
SEMFEG	Hitachi	Su-70
SOI substrate	University Wafer	ID :3213
Strontium chloride hexahydrate	Sigma-Aldrich	10025-70-4
SYLGARD TM 184 Silicone Elastomer Kit	Dow	.000000840559
SYLGARD TM 184 Silicone Elastomer Curring Agent	Dow	.000000840559
Tetraethyl orthosilicate	Aldrich	78-10-4
Tubular Furnace	Carbolite	PTF 14/75/450
Vibrometer	Polytec	OFV-500D
2D XRD	Bruker	D8 Discover	Equipped with a Eiger2 R 500 K 2D detector