Nanomechanical Pyrolytic Carbon Resonators: Novel Fabrication Method and Characterization of Mechanical Properties

Maksymilian Kurek,Peter Larsen,Stephan Keller,Frederik Larsen,Anja Boisen,Silvan Schmid

doi:10.3390/s16071097

Maksymilian Kurek, Peter Larsen + Show 4 more

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https://doi.org/10.3390/s16071097

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Abstract

Micro- and nanomechanical string resonators, which essentially are highly stressed bridges, are of particular interest for micro- and nanomechanical sensing because they exhibit resonant behavior with exceptionally high quality factors. Here, we fabricated and characterized nanomechanical pyrolytic carbon resonators (strings and cantilevers) obtained through pyrolysis of photoresist precursors. The developed fabrication process consists of only three processing steps: photolithography, dry etching and pyrolysis. Two different fabrication strategies with two different photoresists, namely SU-8 2005 (negative) and AZ 5214e (positive), were compared. The resonant behavior of the pyrolytic resonators was characterized at room temperature and in high vacuum using a laser Doppler vibrometer. The experimental data was used to estimate the Young’s modulus of pyrolytic carbon and the tensile stress in the string resonators. The Young’s moduli were calculated to be 74 ± 8 GPa with SU-8 and 115 ± 8 GPa with AZ 5214e as the precursor. The tensile stress in the string resonators was 33 ± 7 MPa with AZ 5214e as the precursor. The string resonators displayed maximal quality factor values of up to 3000 for 525-µm-long structures.

Highlights

The dynamic development in the field of micro- and nanofabrication allowed the definition of a class of ultrasensitive micro- and nanomechanical sensors capable of detecting various physical variables [1]
We investigate pyrolytic carbon as a material for the fabrication of nanomechanical resonators
Our goal was (i) to demonstrate a simple and reliable fabrication process for pyrolytic carbon strings and cantilevers in only three processing steps consisting of photolithography, dry etching and pyrolysis and (ii) to explore the mechanical properties of the resulting structures in order to investigate the influence of processing conditions

Summary

Introduction

The dynamic development in the field of micro- and nanofabrication allowed the definition of a class of ultrasensitive micro- and nanomechanical sensors capable of detecting various physical variables [1]. The high sensitivity of these sensors is a great opportunity, in particular for mass [2], force [3] and thermal [4] sensing for numerous applications such as mass spectrometry [5], cell detection [6] and infra-red (IR) spectroscopy [7] These devices typically consist of simple micromechanical structures such as singly-clamped cantilever beams or doubly-clamped bridges that exhibit resonant behavior. Micro- and nanomechanical resonators are typically fabricated from low-loss semiconductor materials and ceramics, such as silicon, silicon nitride, silicon carbide or aluminum nitride The structuring of these materials requires a photolithography step and a chemical or physical etch. For the realization of micro- and nanoelectromechanical systems, the micromechanical resonators should preferentially be electrically conductive, which requires additional doping in the case of semiconductors and metallization in the case of ceramics

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