(Invited) Suspended 1D/2D Nanomaterials: Progress on a Waferlevel Technology and Applications
Authors: Hermann Sascha , Böttger Simon , Hartmann Martin 
Published: February 2024

The use of 1D and 2D nanomaterials in emerging electronics and sensor technologies is becoming increasingly important due to their unique properties. Here we would like to highlight a scalable process for suspended nanomaterials that provides additional scope for the development of device properties that can be used in advanced concepts ranging from molecular sensing to quantum applications [1]. For example those applications benefit from arrangements as CNT-based nanoresonators with extremely high quality factors [2] usable for quantum bits with long coherence time [3] or suspended sensing nanomaterials for ultra-low power and extremely sensitive gas sensors [4]. Moreover, straining allows to tune intrinsic physical properties of nanomaterials. Thus, the strain-dependence of the band gap (e.g. CNTs <100meV/% [5], MoS2 ~60meV/% [6],) paves the way for integrated-, highly-efficient-, and tunable light sources for on-chip spectrometry in the context of photonic integrated circuits (PICs), as recently reviewed in [7].
Our technological solution to manufacture suspended nanomaterials is aligned with established semiconductor processing chains on 200 mm wafer level and is developed to be modular integrable and compatible with MEMS, MEOMS or CMOS technologies [8]. Along the process chain, we demonstrate wafer-validated deposition processes for semiconducting CNT films which properties can be adjusted with respect to density and even alignment. In particular, for straining aligned CNTs as well as any transferable 2D nanomaterial, we implemented a stressed functional SiO2/SiN layer stack arranged on embedded sacrificial Cu-structures on the wafer surface. After contacting of the nanomaterial and release of sacrificial elements, stressed layers relax, strain and suspend the nanomaterial. This surface engineering approach greatly simplifies the introduction of strain into nanomaterials and makes it accessible for arbitrary device numbers on wafers as well as for monolithic 3D electronic concepts. Unique features include in-plane strains that are applicable in multiaxial directions and can be controlled by designing only two lithography planes. We show that devices with CNTs strained up to 1% determined from Raman spectral analysis, have a positive impact on sensor operation. We show application examples such as a mechanical stress sensor with extremely low on-set sensitivity.
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