Suspended Silicon Beams Research Articles

Reliably straining suspended van der Waals heterostructures

2D materials provide a rapidly expanding platform for the observation of novel physical phenomena and for the realization of cutting-edge optoelectronic devices. In addition to their peculiar individual characteristics, 2D materials can be stacked into complex van der Waals heterostructures, greatly expanding their potential. Moreover, thanks to their excellent stretchability, strain can be used as a powerful control knob to tune or boost many of their properties. Here, we present a novel method to reliably and repeatedly apply a high uniaxial tensile strain to suspended van der Waals heterostructures. The reported device is engineered starting from a silicon-on-insulator substrate, allowing for the realization of suspended silicon beams that can amplify the applied strain. The strain module functionality is demonstrated using single- and double-layer graphene layers stacked with a multilayered hexagonal boron nitride flake. The heterostructures can be uniaxially strained, respectively, up to ∼1.2% and ∼1.8%.

Net on-chip Brillouin gain based on suspended silicon nanowires

The century-old study of photon–phonon coupling has seen a remarkable revival in the past decade. Driven by early observations of dynamical back-action, the field progressed to ground-state cooling and the counting of individual phonons. A recent branch investigates the potential of traveling-wave, optically broadband photon–phonon interaction in silicon circuits. Here, we report continuous-wave Brillouin gain exceeding the optical losses in a series of suspended silicon beams, a step towards selective on-chip amplifiers. We obtain efficiencies up to the highest to date in the phononic gigahertz range. We also find indications that geometric disorder poses a significant challenge towards nanoscale phonon-based technologies.

A high-temperature MEMS heater using suspended silicon structures

A high-temperature MEMS heater using suspended serpentine silicon beams as a filament is proposed for an infrared light source. The MEMS heater utilizes suspended silicon beams for thermal isolation and the mechanical support of heat resistors, and Pt/Ti layers for a Joule heating resistor deposited onto suspended silicon beams. An SiO2 insulator layer was deposited to provide electrical isolation between the thermal resistor and the silicon substrate. The proposed MEMS heater did not require a closed membrane-based back-cavity structure for thermal isolation. The heater is capable of being simply fabricated by a single photolithography process and subsequent silicon anisotropic etching and metal deposition processes. The fabrication process and driving characteristics of the MEMS heater are described. High temperature achieved by the heater was measured by IR camera image processing.

Silicon-based nanoelectronics and nanoelectromechanics

We demonstrate Coulomb blockade oscillations in different single-electron devices in Silicon-On-Insulator (SOI) films up to temperatures of 300 K. The layer sequence in SOI allows the underetching of these devices in order to realize suspended, highly doped silicon nanostructures. Similar suspended silicon beams are fabricated to form novel nanomechanical resonators that can be excited at radio frequencies up to about 300 MHz. Controlling the vibration frequency by a side-gate voltage, these resonators allow charge detection with a sensitivity of 0.1e/Hz, comparable to that of cryogenic single-electron devices.

Fabrication of nanoelectromechanical systems in single crystal silicon using silicon on insulator substrates and electron beam lithography

We have demonstrated a process for fabricating nanometer-scale electromechanical structures of diverse geometries in single crystal silicon, using silicon on insulator substrates. We pattern the substrate using high resolution electron beam lithography with 100 keV electrons followed by Al evaporation and liftoff. The Al is used as an etch mask in CF4 reactive ion etching to pattern the top silicon layer. We then undercut structures using a buffered oxide etch. The structures were made from substrates having a top silicon thickness of 200 or 50 nm, and a buried oxide thickness of 400 nm. With this process we have made a variety of movable structures. We describe the performance of an electrostatically driven Fabry–Perot interferometer that consists of a μm sized pad suspended by wires that are 100–200 nm wide. We have also made much smaller mechanical structures such as suspended silicon beams as narrow as 30 nm.

Integrated silicon process for microdynamic vacuum field emission cathodes

An integrated silicon process has been developed to produce self-aligned gated field emitters on suspended and movable single-crystal silicon beams. The field emitter fabrication process is compatible with an extended version of the single crystal reactive etching and metallization (SCREAM) process. The extended SCREAM process has been used to produce silicon stages with three-dimensional (3D) translation (x,y,z) using integrated capacitive actuators and sensors. Here, we outline the field emitter fabrication process, the extended SCREAM process, and process integration. The integrated structural scheme includes the suspended field emitters integrated with the 3D translator. Electrical isolation and metal contacts are also incorporated with multiple, suspended silicon beams to provide electrical interconnects and isolation of the integrated tips, gate electrodes, actuators, and sensors. The stage with integrated field emitters, translators, isolation, and interconnects is a new approach to the 3D precision positioning and scanning of field emitter tips or scan probes.