News Column

Patent Issued for Sensor and Method for Its Production

June 25, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Benzel, Hubert (Pliezhausen, DE); Armbruster, Simon (Gomaringen, DE); Hoechst, Arnim (Reutlingen, DE); Schelling, Christoph (Stuttgart, DE); Feyh, Ando (Tamm, DE), filed on April 23, 2007, was published online on June 10, 2014.

The assignee for this patent, patent number 8749013, is Robert Bosch GmbH (Stuttgart, DE).

Reporters obtained the following quote from the background information supplied by the inventors: "DE 101 14 036 describes a method for producing micropatterned sensors, in which openings are introduced into a semiconductor substrate, which transform themselves into cavities underneath a sealed diaphragm cover in the depth of the substrate in a subsequent thermal treatment. This makes it possible to produce a capacitive pressure sensor, the cavity in the substrate being developed between two doping zones, which form a plate-type capacitor having a capacitance as a function of the spacing of the doping zones. The doping zones are connected to a corresponding evaluation circuit by deep contacting.

"DE 10 2004 043 357 describes a method for producing a cavity in a semiconductor substrate, in which a lattice-type structure on the surface of the substrate is first produced from substrate material not rendered porous, between which or underneath which a porous region is subsequently formed into the depth of the semiconductor substrate. The porosified region is relocated into a cavity by a subsequent thermal treatment, the lattice-like structure being developed into a diaphragm or into part of a diaphragm above the cavity, if appropriate.

"However, such production methods often do not allow the development of more complex sensors having high resolution and low noise."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "In contrast, the micropatterned sensor according to example embodiments of the present invention and the method for its production have a number of advantages. At least one, preferably several sensor elements that are laterally set apart are formed within a substrate, each being suspended underneath a diaphragm made of dielectric material. The sensor elements may be diodes, in particular, but basically also transistors, for example. Important is that the individual sensor elements have a temperature-dependent electric characteristic whose values are able to be read out via lead wires.

"The individual sensor elements are suspended in one or several cavities formed underneath the diaphragm. In this context, a separate cavity may be provided for each sensor element, or several or all of the sensor elements may be disposed within one shared cavity.

"The individual sensor elements are contacted via lead wires, which run within, on top of or underneath the diaphragm. The diaphragm may be patterned such that it forms individual suspension springs, which link each sensor element to the surrounding mainland or to surrounding webs of an epitaxy layer formed on top of or above the substrate.

"According to an example embodiment, reinforcements, specifically LOCOS (local oxidation of silicon) reinforcements produced by local oxidation, are formed in the dielectric layer constituting the diaphragm, which increase the mechanical stability considerably. The reinforcements may be formed especially at the lateral edge of the diaphragm, so that they surround the particular sensor element; furthermore, they may extend at the lateral edge of the mainland or the remaining webs supporting the sensor elements and thereby accommodate the suspension springs with high stability. The ultimate tensile strength of the suspension springs at the sensor elements and the mainland or the remaining webs is able to be increased in this manner.

"Because of the diaphragm, in particular because of the suspension springs in the diaphragm, excellent thermal decoupling of the sensor elements with respect to each other and the mainland is achieved. Developing the sensor elements in an epitaxial and thus monocrystalline layer makes it possible to keep the signal noise very low. This is advantageous in particular when forming diodes or transistors.

"Thus, a component array having high resolution or a high number of sensor elements and low noise is formed, which may have a mechanically very sturdy design. The individual lead wires to the sensor elements can be connected to shared lead wires, so that the individual components may be read out via successive addressing. Due to the high integration, the power requirement is low.

"In particular, this makes it possible to produce a diode array for the spatially resolved temperature measurement and/or for the spectroscopic measurement of a gas concentration. Another field of application is a fingerprint sensor.

"According to an example embodiment, the sensor not only includes the detector region having the sensor elements but, laterally adjacent and advantageously isolated therefrom, a circuit region including additional components to evaluate the signals output by the sensor elements. At least a few of the process steps of forming the sensor elements of the detector region may also be utilized to produce the circuit region, so that a rapid and cost-effective production is possible. Thus, a MEMS (micro electro mechanical system) component having a combined sensor system and electronic evaluation circuit is able to be formed on one chip.

"The production may be implemented entirely by surface-micromechanical process steps, so that only one surface needs to be processed. The production may be implemented at the level of the wafer with subsequent sectioning.

"To begin with, a first region of the doped substrate (or a doped layer formed on the substrate) is rendered porous for the production, a lattice-like structure and a second region surrounding the first region first being protected from the subsequent etching process by suitable doping. Thus, the first region underneath the lattice-type structure may subsequently be rendered selectively porous in electrolytic manner; if appropriate, complete removal of the material in this region is also possible already. An epitaxial layer may then be grown on the lattice-like structure and the surrounding mainland, annealing of the porous region being implemented during the growing process (or possibly also in an additional step) while forming a cavity.

"Thus, an epitaxial monocrystalline layer in which the sensor elements are subsequently developed by additional process steps, e.g., by doping corresponding diode regions, may be formed above the cavity. Since the sensor elements are developed in the monolithic epitaxial layer, they exhibit low signal noise. The cavity already thermally insulates them from the substrate.

"Further insulation is achieved by developing a diaphragm underneath which the sensor elements are suspended. To this end, one (or several) dielectric layer(s) is/are applied on the epitaxy layer and then patterned. In particular, the dielectric layer may be formed by oxidation or deposition of an oxide layer, formation of etching accesses through the dielectric layer and the epitaxy layer, as well as subsequent sacrificial layer etching of the epitaxy layer. The at least one dielectric layer thus forms a diaphragm, which is self-supporting above the cavity and accommodates the particular sensor element in thermally and mechanically decoupled manner. Further thermal decoupling may be achieved by patterning suspension springs in the diaphragm, thereby making it possible to route the electrical lead wires to the sensor elements via the suspension springs.

"Example embodiments of the present invention are explained in greater in the following text with the aid of the accompanying drawing."

For more information, see this patent: Benzel, Hubert; Armbruster, Simon; Hoechst, Arnim; Schelling, Christoph; Feyh, Ando. Sensor and Method for Its Production. U.S. Patent Number 8749013, filed April 23, 2007, and published online on June 10, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8749013.PN.&OS=PN/8749013RS=PN/8749013

Keywords for this news article include: Electronics, Semiconductor, Robert Bosch GmbH.

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Source: Electronics Newsweekly


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