1. Preparation of the solution
2. Preparation of polydimethylsiloxane (PDMS) templates
3. Gel film deposition on SOI (100) substrates by dip-coating
4. Surface micro/nanostructuration by soft imprint lithography
5. Gel film crystallization by thermal treatment
6. Designing of lithography mask layout
The mask used in this process is designed specifically for a device fabrication on the SOI substrate with epitaxial nanostructured quartz. All the fabrication processes are carried out on the quartz side. The mask was designed in a way that negative tone resist needs to be used in each step. The mask is organized in four different steps as explained below.
7. Cleaning of the quartz samples for the cantilever microfabrication process with piranha solution
8. Step 1: Patterning cantilever shape on the quartz thin film
9. Step 2: Realization of bottom and top electrode
10. Step 3: Patterning the sample to etch Si(100) layer
11. Step 4: Releasing cantilever by wet chemical etching of SiO2
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 (Figure 2d). We also analyzed the detailed crystallization of quartz pillars using electron diffraction technique and FEG-SEM images in the backscattered electrons mode (Figure 2e-f). A deeper structural characterization of a single quartz-based piezoelectric nanostructured cantilevers was performed by recording the pole figure and rocking curve as shown in Figure 2g-i. The Electromechanical response of the quartz-based piezoelectric cantilevers was detected using both (i) a Laser Doppler Vibrometer (LDV) equipped with laser, photodetector and frequency generator (see Figure 2j) and (ii) an atomic force microscope in which the AC drive output of a Lock-in Amplifier (LIA) is fed to the top and bottom electrodes of the cantilever, while the vibration is recorded with the Optical Beam Deflection System of the AFM (see Figure 2k,l). Notice that the vibrometer was used in the displacement mode with a range of 50 nm/V. The frequency generator utilized to actuate the inverse-piezoelectricity of quartz cantilever was an arbitrary waveform generator.
Figure 1: Device fabrication. General schematics and FEG-SEM images of the synthesis and microfabrication steps of quartz cantilever. (a) Dip coating multilayer deposition of Sr-silica solution on SOI substrate is followed by nanostructuring of the film with NIL process (B,c,d). (e) annealing of the sample at 1000 °C in the air atmosphere enables the crystallization of nanostructured quartz film. Finally, a nanostructured quartz cantilever is fabricated with silicon micromachining (f,g,h,i). Please click here to view a larger version of this figure.
Figure 2: (a) SEM image of a nanostructured quartz-based chip with different cantilever dimensions. (b) SEM image of a single nanostructured quartz cantilever (36 µm large and 70 µm long). (c) Cross sectional FEG-SEM image of nanostructured quartz film on SOI substrate. (d) 2D X-ray diffraction pattern of the nanostructured cantilever. Notice that the different layers together with their thicknesses are indicated in the diffractogram. (e) FEG-SEM top image of nanostructured quartz film. (f) Higher resolution TEM image of a single quartz pillar. The inset shows the single crystal nature of the pillar resolved by electron diffraction. (g) 2D pole figure of α-quartz(100)/Si(100) cantilever. (h) Optical image of the whole chip during microdiffraction measurements pointed by a laser beam. Notice that the green color in the optical image corresponds to the diffraction of the natural light produced by the interaction of light and the quartz nanopillar that act as a photonic crystal. (i) Rocking curve of the quartz/Si cantilever showing a mosaicity value of 1.829° of the (100) quartz reflection. (l) Mechanical characterization by noncontact vibrometry measurements under low vacuum of a quartz-based cantilever of 40 µm large and 100 µm long composed of a 600 nm thick patterned quartz layer. The nanopillars diameter and separation distance are 400 nm and 1 µm, respectively and the thickness of the Si device layer is 2 µm. The inset image shows the linear dependence of the cantilever amplitude and applied AC voltage. (k,l) Atomic Force Microscopy measurements in which the AC drive output of a Lock-in Amplifier (LIA) is fed to the top and bottom electrodes of the sample, while the vibration is recorded with the Optical Beam Deflection System of the AFM, i.e., LIA’s amplitude versus time for different applied voltage amplitudes (from 2 to 10 VAC). Notice that we observed similar linear dependence of the cantilever displacement in nanometers and applied AC voltage. Please click here to view a larger version of this figure.
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 |
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.
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.
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.