AlGaN/GaN high electron mobility transistor structures for pressure and pH sensing

Nitride High Electron Mobility Transistor(HEMT) structures are excellent candidates for polar liquid detectors, pressure sensors and piezoelectric-related applications. The changes in conductance of the channel of AlGaN/GaN high electron mobility transistor structures during application of both tensile and compressive strain are reported. For fixed Al mole fraction, the changes in conductance were roughly linear over the range up to 2.7x 10(8)N.cm(-2), with coefficients for planar devices of -6.0 +/-2.5 x 10(-10) S.N-1 m(-2) for tensile strain and +9.5+/-3.5 x 10(-10) S.N(-1)m(-2) for compressive strain. The large changes in conductance demonstrate that simple AlGaN/GaN heterostructures are promising for pressure and strain sensor applications. A gateless HEMT structure was also used for sensing different liquids present in the gate region. The forward current showed significant decreases upon exposure of the gate area to solvents (water, acetone) or acids (HCl). Milli ampere changes in the source-drain current are observed relative to the value measured in air ambient. The pH sensitivity is due to changes in net surface charge that affects the relative depletion in the channel of the transistor.