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Researchers Submit Patent Application, "Microelectromechanical Component and Method for Producing a Microelectromechanical Component", for Approval

May 8, 2014



By a News Reporter-Staff News Editor at Politics & Government Week -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Schelling, Christoph (Stuttgart, DE); Lutz, Theresa (Mannheim, DE), filed on October 15, 2013, was made available online on April 24, 2014.

The patent's assignee is Robert Bosch GmbH.

News editors obtained the following quote from the background information supplied by the inventors: "The present disclosure relates to an MEMS component and a method for producing an MEMS component. In particular, the present disclosure relates to such an MEMS component which comprises a charge-storing layer in its construction.

"Microelectromechanical components, designated as MEMS components for short hereinafter, are electromechanical components having extremely small dimensions in the micrometers range. Such systems can be used both as sensors and as actuators.

"As sensors, such MEMS components are used for example in microphones, in which a small deflection of a microphone membrane is intended to be converted into an electrical signal. Furthermore, such sensors are frequently used within identifying vibrations or shocks. Moreover, such elements can be used as acceleration sensors, in order for example to trigger an airbag of a motor vehicle in the case of an accident.

"Furthermore, such MEMS components are also used as actuators. They are used for example for realizing extremely small drives or are used in print heads of inkjet printers.

"FIG. 1 shows a schematic illustration of an MEMS component in accordance with the prior art such as can be used for electret microphones. In this case, such a conventional MEMS component comprises two electrodes 1 and 4 spaced apart from one another. In this, one of the two electrodes, here the top electrode 4, is usually movable. By contrast, the other electrode, here the bottom electrode 1, is usually arranged in a fixed manner. An insulating layer 2 is arranged on the bottom electrode 1 in a manner facing in the direction of the top electrode 4. Furthermore, a charge-storing layer 3 is arranged on said insulating layer 2 once again in a manner facing in the direction of the top electrode 4. If the distance between the bottom electrode 1 and the top electrode 4 is varied, then a charge outflow will be measured as current via a measuring resistor.

"In this case, by way of example, organic electrets on the basis of polymers are used as materials for the charge-storing layer 3. The European Patent Application EP 2 400 515 A discloses an amorphous fluoropolymer under the trade name CYTOP. Furthermore, further polymer-based electrets are also known. By way of example, polytetrafluoroethylene (PTFE) is frequently also used as an electret for MEMS components.

"In addition, there are also further approaches with electrets based on inorganic materials. US 3,946,422 discloses, for example, a construction for an MEMS component, silicon dioxide (SiO.sub.2) or titanium dioxide (TiO.sub.2) being mentioned as electret for the charge-storing layer.

"In the case of conventional electrets, the charge stored in the charge-storing layer decreases over time. Therefore, the function of the MEMS component can be impaired, for example at high temperatures or high air humidities.

"Furthermore, the charge stored in the case of conventional electrets is locally immobile. Therefore, there is the problem that within the charge-storing layer a highly non-uniform distribution can form both into the depth and within the layer plane of the stored charge. Moreover, the confinement energy which has to be applied in order to mobilize charges from the electret is neither very high nor well defined, but rather has a certain energetic distribution. Therefore, a discharge can easily occur, which impairs the long-term stability and reliability of the MEMS component.

"Therefore, there is a need for an MEMS component having a charge-storing layer with long-term stability. In particular, there is a need for an MEMS component in which the charge-storing layer has a high temperature and moisture insensitivity.

"Furthermore, there is a need for an MEMS component having a charge distribution that is as uniform as possible and well defined both energetically and spatially within a charge-storing layer which, with respect to the surrounding dielectric layers, forms high confinement energy barriers for charges."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "In accordance with a first aspect, the disclosure provides a microelectromechanical component, comprising a first electrically conductive substrate; a second electrically conductive substrate, which is arranged in a manner spaced apart from the first electrically conductive substrate; a first dielectric layer, which is arranged on a side of the first conductive substrate which faces in the direction of the second electrically conductive substrate; a charge-storing layer, which is arranged on the first dielectric layer; and a second dielectric layer, which is arranged on the charge-storing layer.

"In accordance with a further aspect, the present disclosure provides a method for producing a microelectromechanical component comprising the following steps: providing a first electrically conductive substrate; applying a first dielectric layer to the first electrically conductive substrate; applying a charge-storing layer to the first dielectric layer; applying a second dielectric layer to the charge-storing layer; providing a second electrically conductive substrate in a manner spaced apart from the first electrically conductive substrate; applying an electrical voltage between the first electrically conductive substrate and the second electrically conductive substrate; and charging the charge-storing layer.

"A concept of the present disclosure involves the charge-storing layer being completely surrounded by electrically insulating, dielectric materials. For this purpose, the charge-storing layer is surrounded by the dielectric layers on both sides. Consequently, the charge-storing layer is no longer separated from the opposite electrode only by an air space, but rather is additionally protected by at least one electrically insulating material.

"A considerable advantage is afforded by the fact that it is considerably more difficult for the charge carriers stored in the charge-storing layer to be able to leave the charge-storing layer. Consequently, the charge stored in said charge-storing layer is maintained significantly better. In particular, this also reduces the sensitivity toward loss of charge in an environment with high air humidity and/or temperature.

"The fact that, with the construction according to the disclosure, an energetically better defined confinement of the charge carriers within the charge-storing layer can be achieved through the choice of suitable dielectric layers with correspondingly high energy barriers for the charges is also particularly advantageous. This likewise has an advantageous effect on the function of the MEMS component.

"In accordance with one embodiment, the charge-storing layer is a polycrystalline layer. A large number of charge carriers can be stored with long-term stability in a polycrystalline layer. Furthermore, the charge carriers can move freely within the polycrystalline layer. A particularly uniform distribution of the stored charge carriers in the layer is thus possible.

"In an alternative embodiment, the charge-storing layer is a layer composed of nanocrystals embedded into a dielectric. Such nanocrystals likewise enable electrical charge carriers to be stored with long-term stability.

"In a further embodiment, an electrically insulating sealing layer is arranged on the second dielectric layer. Said sealing layer firstly protects the construction situated underneath against mechanical influences. Furthermore, said sealing layer also additionally improves the insulating properties of the second dielectric layer. Consequently, the charge carriers stored in the charge-storing layer are additionally protected.

"In a further embodiment, a ferroelectric layer is arranged on the second electrically conductive substrate. Such a ferroelectric layer additionally shields the second electrically conductive substrate from the first electrically conductive substrate with the layers arranged thereon and furthermore also improves the effects arising as a result of the relative movement of the two electrically conductive layers in relation to one another.

"In one embodiment, an electrically insulating sealing layer is arranged on the ferroelectric layer. Said sealing layer protects the construction sited underneath. If the MEMS component according to the disclosure does not comprise a ferroelectric layer, said sealing layer can also be applied to the second electrically conductive substrate.

"In accordance with one embodiment, in the method for producing an MEMS component, the step for charging the charge-storing layer comprises a step for displacing the first electrically conductive substrate relative to the second electrically conductive substrate. During this displacement of the two substrates, all regions of the construction on the first substrate progressively come into contact with regions on the second substrate. Consequently, all regions of the charge-storing layer can be charged with charge carriers.

"In a further embodiment, the method furthermore comprises a step in which a sealing layer is deposited after the step of charging the charge-storing layer. Consequently, said sealing view particularly reliably prevents the stored charge carriers from being discharged.

BRIEF DESCRIPTION OF THE DRAWINGS

"Further features and advantages of the embodiments of the disclosure are evident from the following description with reference to the accompanying drawings.

"In the figures:

"FIG. 1 shows a schematic illustration of a cross section through an MEMS component in accordance with the prior art;

"FIG. 2 shows a schematic illustration of a cross section through an MEMS component in accordance with one embodiment of the present disclosure;

"FIG. 3 shows a schematic illustration of a cross section through an MEMS component in accordance with a further embodiment of the disclosure;

"FIG. 4 shows a schematic illustration of a cross section through an MEMS component in accordance with a further embodiment of the disclosure;

"FIG. 5 shows a schematic illustration of a plan view of an MEMS component in accordance with one embodiment of the present disclosure;

"FIG. 6 shows a schematic illustration of a method for producing an MEMS component in accordance with one embodiment of the disclosure."

For additional information on this patent application, see: Schelling, Christoph; Lutz, Theresa. Microelectromechanical Component and Method for Producing a Microelectromechanical Component. Filed October 15, 2013 and posted April 24, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5500&p=110&f=G&l=50&d=PG01&S1=20140417.PD.&OS=PD/20140417&RS=PD/20140417

Keywords for this news article include: Robert Bosch GmbH.

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