The electrical characteristics of a Pd/AIN/Si thin film hydrogen gas sensor

We have extended our previous investigation of the electrical characteristics of a Pd/AlN/Si thin film sensor for varying thicknesses of AlN, from 300-2000Angstrom. The capacitance vs. voltage, C(V), and conductance vs. voltage, G(V), measurements were utilized to investigate the presence of surface states within the Si gap at the AlN/Si interface. Our previous experiments on 500Angstrom AlN did show the presence of interface traps, with an estimated surface density between 8x10(14) and 15x10(15) m(-2) eV(.1) [1]. in our present work, we've extended this investigation to devices with AlN thicknesses varying from 250 to 2000Angstrom. The density of these states is shown to be a slowly varying function of the position in the gap, but is a strong function of the thickness of the AlN film. The density of these states ranged from about 30x10(15) M(-2)eV(-1) for the 250Angstrom device, to about 1.7x10(15) m(-2)eV(-1) for thicknesses up to 2000Angstrom. The distribution of these states is not affected by high temperature annealing. While the presence of hydrogen is sensed simply by a shift in the flat band bias, these surface states are not affected.