Monolayer graphene exhibits exceptional electronic and mechanical properties, making it a very promising material for nanoelectromechanical devices. Here, we conclusively demonstrate the piezoresistive effect in graphene in a nanoelectromechanical membrane configuration that provides direct electrical readout of pressure to strain transduction. This makes it highly relevant for an important class of nanoelectromechanical system (NEMS) transducers. This demonstration is consistent with our simulations and previously reported gauge factors and simulation values. The membrane in our experiment acts as a strain gauge independent of crystallographic orientation and allows for aggressive size scalability. When compared with conventional pressure sensors, the sensors have orders of magnitude higher sensitivity per unit area.

A novel pressure sensor based on a suspended graphene membrane is proposed. The sensing mechanism is explained based on tight binding calculations of strain-induced changes in the band structure. A CMOS compatible fabrication process is proposed and used to fabricate prototypes. Electrical measurement data demonstrates the feasibility of the approach, which has the advantage of not requiring a separate strain gauge, i.e. the strain gauge is integral part of the pressure sensor membrane. Hence, graphene membrane based pressure sensors can in principle be scaled quite aggressively in size.

The present paper describes a device structure for controlling and measuring strain in graphene membranes. We propose to induce strain by creating a pressure difference between the inside and the outside of a cavity covered with a graphene membrane. The combination of tight-binding calculations and a COMSOL model predicts strain induced band gaps in graphene for certain conditions and provides a guideline for potential device layouts. Raman spectroscopy on fabricated devices indicates the feasibility of this approach. Ultimately, pressure-induced band structure changes could be detected electrically, suggesting an application as ultra-sensitive pressure sensors.

Pressure sensors based on suspended graphene membranes have shown extraordinary sensitivity for uniaxial strains, which originates from graphene's unique electrical and mechanical properties and thinness [1]. This work compares through both theory and experiment the effect of cavity shape and size on the sensitivity of piezoresistive pressure sensors based on suspended graphene membranes. Further, the paper analyzes the effect of both biaxial and uniaxial strain on the membranes. Previous studies examined uniaxial strain through the fabrication of long, rectangular cavities. The present work uses circular cavities of varying sizes in order to obtain data from biaxially strained graphene membranes.

We demonstrate humidity sensing using a change of the electrical resistance of single-layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N-2), oxygen (O-2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. Density functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. The interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO(2)d substrate leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct electrical readout and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.

A chip to wafer scale, CMOS compatible method of graphene device fabrication has been established, which can be integrated into the back end of the line (BEOL) of conventional semiconductor process flows. In this paper, we present experimental results of graphene field effect transistors (GFETs) which were fabricated using this wafer scalable method. The carrier mobilities in these transistors reach up to several hundred cm(2) V-1 s(-1). Further, these devices exhibit current saturation regions similar to graphene devices fabricated using mechanical exfoliation. The overall performance of the GFETs can not yet compete with record values reported for devices based on mechanically exfoliated material. Nevertheless, this large scale approach is an important step towards reliability and variability studies as well as optimization of device aspects such as electrical contacts and dielectric interfaces with statistically relevant numbers of devices. It is also an important milestone towards introduting graphene into wafer scale process lines.

We report on a wafer scale fabrication of graphene based field effect transistors (GFETs) for use in future radio frequency (RF) and sensor applications. The process is also almost entirely CMOS compatible and uses a scalable graphene transfer method that can be incorporated in standard CMOS back end of the line (BEOL) process flows. Such a process can be used to integrate high speed GFET devices and graphene sensors with silicon CMOS circuits.