Methods of manufacturing thin-film absolute pressure sensors

Abstract

Resistive and capacitive absolute pressure sensors are disclosed which are made by surface micromachining and thin-film techniques. In the case of a capacitive sensor, the electrodes have a high insulation resistance relative to each other, the diaphragm exhibits only little tensile strain in the finished condition, no sublimation step is necessary to prevent the diaphragm from sticking to the substrate, the diaphragm provides a measurement signal over a wide pressure range even if its rests against the substrate, the measurement signal is virtually temperature-independent, and only few chemical-vapor-deposition and photolithographic steps are necessary. The capacitive sensor has a glass substrate and a diaphragm which bound a hermetically sealed cavity, the substrate supporting, on the cavity side, a substrate electrode with first interconnection tracks or corner pads extending therefrom, the diaphragm being made of the material of a first insulating layer, which firmly adheres, at least in part, to the substrate at the edge of the cavity, and supporting, on the side remote from the cavity, a top electrode and a second insulating layer which completely covers the top electrode and the diaphragm and hermetically seals the cavity, and the top electrode having second interconnection tracks extending therefrom onto the first insulating layer outside the diaphragm. In the case of a resistive sensor, the substrate electrode is omitted, and the top electrode is replaced by a half or full bridge consisting of piezoresistors. Four manufacturing process variants are disclosed.