R. G. Beck

Using soft lithography to fabricate GaAs/AlGaAs heterostructure field effect transistors

This letter describes the fabrication of functional GaAs/AlGaAs field effect transistors using micromolding in capillaries—a representative soft lithographic technique. The fabrication process involved three soft lithographic steps and two registration steps. Room temperature characteristics of these transistors resemble those of field effect transistors fabricated by photolithography. The fabrication of functional microelectronic devices using multilayer soft lithography establishes the compatibility of these techniques with the processing methods used in device fabrication, and opens the door for their development as a technique in this area.

GaAs/AlGaAs self-sensing cantilevers for low temperature scanning probe microscopy

We have fabricated scanning probe microscope cantilevers with dimensions 65×11.4×0.25 μm3 and 3×2×0.129 μm3 from GaAs/Al0.3Ga0.7As heterostructures containing two-dimensional electron gases. Deflection is measured by an integrated field-effect transistor (FET) that senses strain via the piezoelectric effect and provides a low noise, low power displacement readout. We present images of a 200 nm mica grating taken with the large cantilever having a deflection (force) noise 10 A/√Hz (19 pN/√Hz) at T=2.2 K. The small cantilever has a resonant frequency of 11 MHz, a FET gate charge noise of 0.001 e/√Hz, and is projected to have a deflection (force) noise of 0.002 A/√Hz (1 pN/√Hz) at T=4.2 K.

Strain‐sensing cryogenic field‐effect transistor for integrated strain detection in GaAs/AlGaAs microelectromechanical systems

We have fabricated a strain‐sensing cryogenic field‐effect transistor (FET) from a GaAs/AlGaAs heterostructure containing a near‐surface two‐dimensional electron gas. The FET has transconductance 100 μS and a small signal drain‐source resistance 10 MΩ. The charge noise has a flat spectrum at high frequencies with magnitude 0.2e/√Hz and 1/f noise corner less than 300 Hz. The piezoelectric effect couples stress in the substrate to the electron density in the FET channel giving an electrical response to applied strain. Strain sensitivity was measured to be 2×10−9/√Hz, limited by FET noise. Integrated strain‐sensing FETs offer advantages for detecting small forces in GaAs/AlGaAs microelectromechanical systems.

Fabrication of arrays of Schottky diodes using microtransfer molding

Abstract This paper describes the application of microtransfer molding—a representative soft lithographic technique—to the fabrication of simple Schottky diodes on silicon. The fabrication of a diode involved two microtransfer molding steps. The current–voltage responses of these diodes displayed characteristic nonlinear diode behavior. The yield of pattern transfer was 95% and the yield of functional diodes was 90%. Future improvements and potential industry application is proposed.

Measuring the mechanical resonance of a GaAs/AlGaAs cantilever using a strain-sensing field-effect transistor

We have fabricated a cantilever with dimensions from a heterostructure containing a two-dimensional electron gas. A strain-sensing field-effect transistor (FET) integrated into the cantilever base acts as a displacement sensor via the piezoelectric effect. The FET was used to measure the cantilever mechanical quality factor Q = 360 and resonance frequency kHz which is close to kHz calculated from geometry. FETs can be integrated into GaAs/AlGaAs microelectromechanical systems as force and displacement sensors.

Fabrication of GaAs/AlGaAs high electron mobility transistors with 250 nm gates using conformal phase shift lithography

Abstract This paper establishes the feasibility of soft lithography for fabrication of submicron-scale electronic devices. Near-field conformal phase shift lithography — a representative soft lithographic technique — was used on a broadband exposure tool to fabricate the gate fingers of a high electron mobility transistor (HEMT). The gates of this proof-of-concept device had lengths of 250 nm and widths of 40 μm. The device had a transconductance of 4 mS and a current–voltage response similar to that of a conventional HEMT.