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Patent Issued for Planar Cavity MEMS and Related Structures, Methods of Manufacture and Design Structures

May 28, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- According to news reporting originating from Alexandria, Virginia, by VerticalNews journalists, a patent by the inventors Dang, Dinh (Essex Junction, VT); Doan, Thai (Burlington, VT); Maling, Jeffrey C. (Grand Isle, VT); Stamper, Anthony K. (Williston, VT), filed on December 20, 2010, was published online on May 13, 2014.

The assignee for this patent, patent number 8722445, is International Business Machines Corporation (Armonk, NY).

Reporters obtained the following quote from the background information supplied by the inventors: "Integrated circuit switches used in integrated circuits can be formed from solid state structures (e.g., transistors) or passive wires (MEMS). MEMS switches are typically employed because of their almost ideal isolation, which is a critical requirement for wireless radio applications where they are used for mode switching of power amplifiers (PAs) and their low insertion loss (i.e., resistance) at frequencies of 10 GHz and higher. MEMS switches can be used in a variety of applications, primarily analog and mixed signal applications. One such example is cellular telephone chips containing a power amplifier (PA) and circuitry tuned for each broadcast mode. Integrated switches on the chip would connect the PA to the appropriate circuitry so that one PA per mode is not required.

"Depending on the particular application and engineering criteria, MEMS structures can come in many different forms. For example, MEMS can be realized in the form of a cantilever beam structure. In the cantilever structure, a cantilever arm (suspended electrode with one end fixed) is pulled toward a fixed electrode by application of an actuation voltage. The voltage required to pull the suspended electrode to the fixed electrode by electrostatic force is called pull-in voltage, which is dependent on several parameters including the length of the suspended electrode, spacing or gap between the suspended and fixed electrodes, and spring constant of the suspended electrode, which is a function of the materials and their thickness. Alternatively, the MEMS beam could be a bridge structure, where both ends are fixed.

"MEMS can be manufactured in a number of ways using a number of different tools. In general, though, the methodologies and tools are used to form small structures with dimensions in the micrometer scale with switch dimensions of approximately 5 microns thick, 100 microns wide, and 200 microns long. Also, many of the methodologies, i.e., technologies, employed to manufacture MEMS have been adopted from integrated circuit (IC) technology. For example, almost all MEMS are built on wafers and are realized in thin films of materials patterned by photolithographic processes on the top of the wafer. In particular, the fabrication of MEMS uses three basic building blocks: (i) deposition of thin films of material on a substrate, (ii) applying a patterned mask on top of the films by photolithographic imaging, and (iii) etching the films selectively to the mask.

"For example, in MEMS cantilever type switches the fixed electrodes and suspended electrode are typically manufactured using a series of conventional photolithographic, etching and deposition processes. In one example, after the suspended electrode is formed, a layer of sacrificial material, e.g., the spin-on polymer PMGI made by Microchem, Inc., is deposited under the MEMS structure, to form a cavity, and over the MEMS structure to form a cavity. The cavity over the MEM is used to support the formation of a cap, e.g., SiN dome, to seal the MEMS structure. However, this poses several shortcomings. For example, it is known that MEMS cavities formed with spin-on polymers such as PMGI, are non-planar. Non-planar MEMS cavities, though, introduce issues including, for example, lithographic depth of focus variability and packaging reliability due to dielectric cracking. In addition, MEMS cavities formed with spin-on polymers require processing at low temperatures, to avoid reflowing or damaging the polymer; and the polymer can leave organic (i.e., carbon containing) residues in the cavity post venting.

"Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove."

In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "In a first aspect of the invention, a method of forming at least one Micro-Electro-Mechanical System (MEMS) comprise forming a plurality of discrete wires on a substrate. The method further comprises forming a sacrificial cavity layer on the discrete wires. The method further comprises forming trenches in an upper surface of the sacrificial cavity layer. The method further comprises filling the trenches with dielectric material. The method further comprises depositing metal on the sacrificial cavity layer and on the dielectric material to form a beam with at least one dielectric bumper extending from a bottom surface thereof.

"In another aspect of the invention, a method of forming at least one Micro-Electro-Mechanical System (MEMS) comprises forming a wiring layer on a substrate. The method further comprises patterning the wiring layer to form a plurality of discrete wires with spaces therebetween. The method further comprises forming a sacrificial cavity layer on the plurality of discrete wires. The method further comprises planarizing the sacrificial cavity layer. The method further comprises performing a HF clean with photoresist to hydrogen passivate the planarized sacrificial cavity layer. The method further comprises etching the hydrogen passivated planarized sacrificial cavity layer to form at least one trench. The method further comprises forming an oxide material in the at least one trench. The method further comprises depositing an electrode material on the oxide material and the passivated planarized sacrificial cavity layer to form a beam with a oxide material on an underside thereof.

"In yet another aspect of the invention, a structure comprises a plurality of discrete wires on a substrate with spaces therebetween. The structure further comprises a MEMS beam opposing the plurality of discrete wires. The MEMS beam has an oxide peg attached to a bottom surface thereof and extending towards the plurality of discrete wires.

"In another aspect of the invention, a design structure tangibly embodied in a machine readable storage medium for designing, manufacturing, or testing an integrated circuit is provided. The design structure comprises the structures of the present invention. In further embodiments, a hardware description language (HDL) design structure encoded on a machine-readable data storage medium comprises elements that when processed in a computer-aided design system generates a machine-executable representation of the MEMS, which comprises the structures of the present invention. In still further embodiments, a method in a computer-aided design system is provided for generating a functional design model of the MEMS. The method comprises generating a functional representation of the structural elements of the MEMS.

"In particular aspects, the method in a computer-aided design system for generating a functional design model of a MEMS comprises: generating a functional representation of a plurality of discrete wires on a substrate; generating a functional representation of a sacrificial cavity layer on the discrete wires; generating a functional representation of trenches in an upper surface of the sacrificial cavity layer; generating a functional representation of filling the trenches with dielectric material; and generating a functional representation of depositing metal on the sacrificial cavity layer and on the dielectric material to form a beam with at least one dielectric bumper extending from a bottom surface thereof."

For more information, see this patent: Dang, Dinh; Doan, Thai; Maling, Jeffrey C.; Stamper, Anthony K.. Planar Cavity MEMS and Related Structures, Methods of Manufacture and Design Structures. U.S. Patent Number 8722445, filed December 20, 2010, and published online on May 13, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=90&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=4488&f=G&l=50&co1=AND&d=PTXT&s1=20140513.PD.&OS=ISD/20140513&RS=ISD/20140513

Keywords for this news article include: MEMS, Nanotechnology, Emerging Technologies, Microelectromechanical Systems, International Business Machines Corporation.

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Source: Journal of Engineering