Humidity Sensor Based on Partially Oxidized Porous Silicon

Porous silicon (PS) is known to have an highly developed effective surface. The conductivity, dielectric permittivity and other PS electrophysical characteristics depend on structure and can be essentially changed under the influence of moisture. Using an aluminium-PS junction we have realized a surface-type humidity sensor which capacitance changes up to one order of magnitude. The porous layers were prepared from 4 inch (100) oriented n(+)-type antimony doped silicon wafers by anodization in HF/ethanol electrolyte under current densities of 5-50 mA/cm(2). Electrochemical or low temperature thermal oxidation of PS were used to stabilize working characteristics of the sensor. Aluminum film was evaporated directly on the PS layer, then lithography process was performed to form the grids topology of the aluminum contact. The behavior of sensor capacitance on the time was studied during exposure at different relative humidity atmospheres. The response time was about 3-5 min. The sensors showed good stability at the periodic cyclic change of humidity. The presented technology is promising for fabrication of microelectronic sensors sensitive to humidity and different gases.