United Technologies Corporation

Breed Technologies, Inc.

James L Swindal

Robert H Bullis

Daniel H Grantham

Walter J Wiegand, Jr

Charles B Brahm

Arthur G Foyt

Harold D Meyer

Paul L Provenzano

Frank W Gobetz

Robert J Kuhlberg

James R Strife

Richard E Swarts

Robert A Wagner

Mario T Lopiccolo

Donald A Dalton

A silicon capacitive microsensor which is sensitive to acceleration forces includes a silicon capacitive sensing element 10 comprising three silicon layers 12,16,26 having glass dielectric layers 14,24 between each pair of silicon layers with the middle silicon layer 16 consisting of a proof mass 18 suspended between the two glass dielectric layers 14,24 by a silicon hinge 20 which is connected to a slightly thicker silicon support layer 17 around the periphery (FIG. 3 ) between the glass layers 14,24 (FIG. 1 ). Three metallic bond pads 40,42,44 on the surface 45 of the silicon layers 26,16,12, respectively, are soldered to circuit trace pads 108 on a circuit board 100 which has a glass upper layer 104 and a silicon support layer 102. The thermal expansion coefficient between the glass layer 104 and the sensing element 10 are substantially the same, thereby minimizing thermally induced stresses on the sensing element 10 and minimizing inaccuracies associated therewith. Such direct mounting greatly simplifies the manufacturing process for such sensors. Also, such direct mounting eliminates flying leads thereby allowing the sensing element 10 to be fabricated to much smaller dimensions than that of the prior art.

Sensor having direct-mounted sensing element

A silicon capacitive pressure sensor is disclosed that has a glass dielectric material sputter-deposited onto a silicon substrate of the sensor. After deposition of the bulk dielectric material, the glass is patterned and etched to form a pair of concentric rings. An inner ring is of a circular shape, while the outer ring is of an octagonal shape. As compared to prior art dielectric spacers which are of a single ring of relatively wide thickness, the pair of concentric rings disclosed herein significantly reduce the parasitic capacitance of the glass dielectric material, thereby increasing the sensitivity of the sensor.

Capacitive pressure sensor having a reduced area dielectric spacer

A silicon capacitive pressure sensor is disclosed having a silicon substrate and a silicon diaphragm separated by a glass dielectric spacer. The substrate has an upper surface formed as a mesa which is generally curved in shape, the curvature being concave. Due to manufacturing constraints the mesa upper surface comprises a series of concentric rings that approximate the desired concave shape. The step height and diameter of the rings are such that, at full deflection of the diaphragm, the diaphragm touches the center of the mesa, but not the edges of the individual steps. That is, letting the edges or corners of the steps define a curve, the radius of curvature of the diaphragm is smaller than the radius of curvature of the locus of the step corners.

Capacitive pressure sensor having a substrate with a curved mesa

A silicon capacitive pressure sensor is disclosed having a silicon diaphragm and a silicon substrate arranged in parallel and separated by a glass dielectric spacer. The glass is deposited onto a surface of the substrate using an ion milling machine. The sensor further includes a transition piece attached to a second layer of glass insulator disposed between the silicon diaphragm and the transition piece. The transition piece has a throughbore formed therein for applying a fluid to a surface of the silicon diaphragm, the fluid having a pressure desired to be measured by the sensor. The glass disposed between the diaphragm and the transition piece is deposited onto the transition piece using the ion milling process.

Silicon capacitive pressure sensor having a glass dielectric deposited

Manufacturing hinged diaphragms for semiconductor sensors (e.g., accelerometers, pressure transducers, etc.), from a SIMOX wafer (W, FIG. 3 A), in which the internal, insulating, silicon dioxide (SiO.sub.2) layer (3) is used as an etch stop in removing silicon from the underside of the wafer by etching with an appropriately selective etch, producing the reduced thickness, peripheral 'hinge' areas (9; FIG. 3 A to FIG. 3 B), with the exposed part of the silicon dioxide layer being removed in a subsequent etching step (FIG. 3 B to FIG. 3C) using a different, selective etch. This produces a single layer, single-crystal, silicon 'hinge' (9'; FIG. 3C) of uniform, continuous material, enhancing the linearity of diaphragm movement during use and the sensor's sensitivity and accuracy. (See FIG. 4 for methodological steps.) If the top, silicon region of the SIMOX wafer is insufficiently thick for the desired diaphragm thickness, additional layer(s) of epitaxial silicon are grown on the upper side of the silicon crystal until the desired thickness is reached; the same being true for increasing the thickness of the silicon substrate. If having reduced thickness areas for the 'hinge' on both sides of the diaphragm are desired, a SIMOX wafer having an intermediate, silicon dioxide layer on both the 'bottom' and the 'top' of the wafer is used, with each layer serving as an etch stop on its respective side, with the then exposed portions of the silicon dioxide layers thereafter being removed, leaving flanking, alternating, silicon 'hinge' bridges (90a/90b; FIG. 5A-C).

Methodology for manufacturing hinged diaphragms for semiconductor sensors

A micromachined three-plate capacitive accelerometer incorporates a 'sandwich' proof mass formed from two layers that are boron-doped to define hinges attached essentially to the midplane of the proof mass by being placed abutting a bonding interface region at the midplane.

Capacitive accelerometer with mid-plane proof mass

A semiconductive sensor or transducer (100), for example, a pressure sensor utilizing capacitance variations to sense pressure variations, of the silicon-on-silicon type, in which a 'hinge' (111A) in the form of a relatively thin, encircling area is provided at the outer peripheral edge of the diaphragm, causing the central region (117) of the diaphragm (111) to move in a linear, non-curved or planar manner (compare FIG. 2 to FIG. 1), providing a linear response or frequency output. A first embodiment (FIG. 3) of the hinged silicon-on-silicon capacitive pressure sensor, which is basically cylindrical in shape, has the hinge formed by etching, milling or machining away some of the thickness of the diaphragm at its outer peripheral edge. In a second embodiment (FIG. 4) the hinge is formed by etching away some of the thickness of the diaphragm at its outer peripheral edge and using a glass layer to control the etching using a selective chemical enchant which is selective for silicon but does not attack the glass; while a third embodiment (FIG. 5) uses aluminum in place of the glass. In a fourth embodiment (FIG. 6) the hinge is formed effectively on the opposite side of the diaphragm from the shown in the embodiments of FIGS. 3-5. The hinge structure can be used in other forms of semiconductive transducers, which use the relative movement of a semiconductive diaphragm with respect to another semiconductive layer or substrate.

Capacitive semiconductive sensor with hinged diaphragm for planar

Pressure sensors utilizing capacitance variations to sense pressure variations of the silicon-on-silicon type in which dielectric drift, which occurs in such sensors due to the changing characteristics primarily of the dielectric wall support layer (16) extending up from the silicon substrate (12) between it and the silicon diaphragm (11), is minimized by in turn minimizing the contribution of the dielectric layer to the total capacitance of the sensor (10), reducing the dielectric contribution of the capacitance from, for example, about fifty (50%) percent down to a range of no more than about twenty to twenty-five (20-25%) percent and down typically to sixteen to about ten (16%-10%) percent of the total capacitance or lower. Three exemplary approaches are illustrated, namely, etching the outer edges of the dielectric layer, making the wall(s) it form(s) thinner (FIG. 2); reducing the horizontal thickness of the effective peripheral, lower edge(s) of the silicon diaphragm where it interfaces in contact with the wall(s) formed by the dielectric layer (FIG. 3); and/or reducing the horizontal thickness of the effective peripheral, upper edge(s) of the silicon base or substrate where it interfaces with the wall(s) formed by the dielectric layer (FIUG. 4); and/or a combination of one or more of these approaches or any other approach that minimizes the effective capacitive contribution of the peripheral dielectric layer to the total capacitance of the sensor and hence to long term drift.

Capacitive sensor with minimized dielectric drift

A micromachined three-plate capacitive accelerometer incorporates hinges attached to top and bottom surfaces of the proof mass that are symmetric about X and Y axes and also about diagonal axes; passageways for gas film damping in the fixed members that do not affect the capacitance to any significant degree; and provision for independently selecting two of the parameters sensitivity, capacitance and maximum acceleration.

Capacitive accelerometer with separable damping and sensitivity

Capacitive accelerometer with hinges on top and bottom surface

Semiconductor structures for electronic use, such as for example a silicon-glass-silicon pressure sensor (Fig. 3), include mesa or pedestal structures (12A) extending up from silicon substrates (12). In the invention the mesa structures are fabricated in an oxidation process applied in a cyclical fashion (steps 1-3 through 1-5 of Fig. 1). Each cycle includes a photolithographic operation to protect the previously grown oxide on the mesas from etching. During each cycle less oxide is grown (or conversely silicon consumed) on the mesas than in the preceding cycle, while equivalent amounts of oxide are grown on non-mesa areas in each cycle. As a result, the tops of the mesas get higher and higher above the surrounding areas in each cycle. In order to prevent the leaving of any oxide 'scraps' in a non-mesa area during the oxidation steps, resulting from a flaw in the mask, a double exposure process is used, utilizing two completely independent masks, with a positive working photo-resist.

Mesa fabrication in semiconductor structures

A buried laser mirror used in high energy applications provides discrimination between optical signals of different wavelengths and comprises a ceramic substrate bonded to a faceplate that has a multicomponent reflective interlayer formed on the faceplate inner surface. The multicomponent reflective interlayer provides improved thermomechanical properties while maintaining the mirror's optical integrity and includes a metal reflective layer formed on the faceplate inner surface, a diffusion barrier layer fabricated on the metal reflective layer and a surface wetting layer formed on the diffusion barrier layer.

Buried laser mirror with a multicomponent reflective interlayer

A three plate silicon-glass-silicon capacitive pressure transducer includes a conductive silicon diaphragm and substrate relatively spaced by a dielectric body having disposed therein a central electrode positioned between the diaphragm and substrate to form a pressure responsive capacitance with the diaphragm at a value inversely proportional to a pressure signal applied to a pressure sensing surface of the diaphragm.

Three plate silicon-glass-silicon capacitive pressure transducer

A plurality of silicon pressure transducers 10 are formed by processing two conductive silicon wafers 11, 14, one of the wafers including a layer of borosilicate glass 32, a thin portion of which 17 is on the surface 12 of one of the plates of a capacitor formed by field-assisted bonding together of the two wafers, the thin layer of borosilicate glass avoiding arcing during the field-assisted bonding process.

Electrostatic bonded, silicon capacitive pressure transducer

A silicon capacitive pressure transducer 34 comprising two wafers of silicon 14, 32 separated by borosilicate glass 18, 21, one of the wafers 14 having a borosilicate glass pedestal 26 thereon which is metallized 30 to provide one plate of a capacitor, the other plate of which is the surface of one of the silicon wafers 32. The distance between the upper surface of the glass pedestal and the lower surface of the silicon wafer is defined by a portion 18 of the borosilicate glass, the portion 21 of borosilicate glass being the same height as that of the glass pedestal 26. An embodiment of a transducer 34b employs a silicon pedestal 26b, wherein the glass portion 21b only provides separation of the silicon wafers 14b, 32b with lower parasitic capacitance.

Growing community of inventors

East Hampton, CT, United States of America

James L Swindal