Endress U. Hauser Gmbh U. Co.

Endress+hauser Gmbh+co.

Ncr Corporation

Traugott Kallfass

Ernst Luder

Frank Hegner

Hubert Benzel

Joerg Schaepperle

Georg Schneider

Wolfgang Sautter

Walter Koenig

Kenneth R Knight

Ernst Lueder

Gerhard Bader

Masoud Habibi

Christian Borgwardt

Visual displays

In a first variant of this pressure sensor with a substrate and a diaphragm which are joined together parallel to each other in a defined spaced relationship, forming a chamber sealed at least at the edge, the chamber-side surface of the diaphragm is completely covered with a diaphragm electrode. The chamber-side surface of the substrate supports a reference electrode consisting of an outer portion, which extends along the edge of the chamber and whose capacitance is virtually pressure-independent, and a pressure-dependent central portion, which is located at the center of the substrate and is connected with the outer portion via a connecting portion. The remainder of the substrate surface is covered with a measuring electrode spaced from the reference electrode by a constant distance. In a second circular variant and in a third, rectangular variant, the reference electrode consists of an outer portion, which extends along the edge of the chamber and whose capacitance is virtually pressure-independent, and two pressure-dependent central portions, which are each located in one half of the substrate symmetrically with respect to the substrate center and are connected with the outer portion via one connecting portion each, and whose boundary curves are continuous and are optimized by an iterative method. In a third variant, the reference electrode differs from that of the second variant in that it is not centrosymmetrical, but symmetrical with respect to a substrate diameter.

Capacitive pressure sensors with high linearity by optimizing electrode

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.

Methods of manufacturing thin-film absolute pressure sensors

This method comprises the following steps, which are compatible with thin-film technology: forming a bottom electrode (2) on an insulating substrate (1), depositing a humidity-sensitive polymer layer (5) of uniform thickness on the bottom electrode (2) leaving contact areas (3a, 3b) uncovered, activating surface bonds of the polymer layer (5), applying a colloidal dispersion of SiO.sub.2 or Al.sub.2 O.sub.3 particles (6) of uniform grain size as a thin layer to the polymer layer (5) and subsequently drying it, depositing a cover electrode (7) on the particles (6) still evenly distributed on the polymer layer (5) after the drying of the dispersion, and removing the particles (6) together with the portions of the cover electrode (7) overlying them.

Method of manufacturing a capacitive humidity sensor

A moisture sensor is manufactured by applying a thin layer of tantalum oxide to a moisture insensitive substrate and placing at least two electrodes on the tantalum oxide layer. The tantalum oxide layer comprises the oxide of a highly resistive low density tantalum where the tantalum in the layer applied to the substrate has a density of less than 15 g/cm.sup.3. The low density tantalum may be applied by cathode sputtering and the oxide may be formed by anodic oxidation.

Method of manufacturing a moisture sensor

A moisture sensor comprises a moisture-sensitive layer formed from the oxide of highly resistive porous low density tantalum on a moisture-insensitive substrate. Between the substrate and the moisture-sensitive tantalum oxide layer there is a base electrode of an anodically oxidizable metal, preferably tantalum, of a density higher than the density of the low density tantalum from which the tantalum oxide layer is formed. A covering electrode partially covering the tantalum oxide layer has windows through which the water vapor containing medium can penetrate into the moisture-sensitive tantalum oxide layer. The inactive regions of the tantalum oxide layer disposed below the windows are removed to increase the rate of response.

Moisture sensor with valve metal composition electrodes

A moisture sensor including a thin layer of tantalum oxide applied to a moisture insensitive substrate and at least two electrodes placed on the tantalum oxide layer spaced apart from each other wherein the tantalum oxide layer comprises the oxide of a highly resistive low density tantalum where the tantalum in the layer applied to the substrate has a density of less than 15 g/cm.sup.3.

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Grossbottwar, Germany

Traugott Kallfass