News Column

Patent Issued for Vertical Integrated Circuit Switches, Design Structure and Methods of Fabricating Same

August 13, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- A patent by the inventors Anderson, Felix P. (Colchester, VT); Cooney, III, Edward C. (Jericho, VT); McDevitt, Thomas L. (Underhill, VT); Stamper, Anthony K. (Williston, VT), filed on September 16, 2013, was published online on July 29, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8791778 is assigned to International Business Machines Corporation (Armonk, NY).

The following quote was obtained by the news editors from the background information supplied by the inventors: "Integrated circuit switches used in 3D and other 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 due to 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 was not required.

"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. More specifically, the fabrication of MEMS use 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. In any of these methodologies, the switches are fabricated in a horizontal orientation above the wafer/chip.

"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 single cantilever structure such as, for example, shown in U.S. Pat. No. 5,578,976. In this cantilever application, a single cantilever arm (suspended electrode) is pulled toward a fixed electrode by application of a voltage. To manufacture such a cantilever structure, though, several extra and expensive processing steps are required, in addition to the building of the CMOS structure itself. For example, once all of the CMOS wiring is completed, additional process steps are required to form the MEMS switch, which adds considerable processing costs to the structure.

"Also, as clearly shown in such application, the MEMS are horizontal cantilever type switches fabricated above the wafer/chip. These horizontal cantilever type switches are known to add costs to the fabrication of the device, as well as adding to package interaction issues. In addition, horizontal cantilever type switches, in many current applications, are known to stick, e.g., exhibit an inability to open the switch due to freezing closed during processing and the relatively small contact or actuation gap used in the switch, which on the order of 1 micron. This is known as sticktion.

"Additionally, in known applications, the voltage required to pull the suspended electrode down to the fixed electrode by electrostatic force may be high. This has been seen to cause unwanted charging on the insulator after prolonged use and eventual failure of the switch. In certain applications, the high voltage, e.g., 100 volts, is also difficult to obtain since this has to be stepped up from about 1.5-5 volts to 30 to 100 volts using charge pumping or similar methods . The minimum voltage required for switching 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.

"Reducing the pull-in voltage without decreasing the gap and without softening the spring is desirable, as the spring provides the restoring force and determines the switching speed. In U.S. Pat. No. 7,265,429, a pair of side parallel-plate electrostatic actuators is implemented for lowering or eliminating of the bias voltages. These additional electrostatic actuators are used to reduce or eliminate the bias voltage to be applied on the fixed signal electrode. In implementation, the fixed electrode of the side parallel-plate electrostatic actuators can be elevated above a fixed signal electrode. Thus due to a smaller gap, the pull-in voltage required to pull the suspended electrode down to the fixed electrode can be lowered. However, the MEMS shown in U.S. Pat. No. 7,265,429 are not hermetically sealed, and the additional electrostatic actuators can increase fabrication costs. Also, the MEMS are horizontal cantilever type switches fabricated above the wafer/chip.

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

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "In an aspect of the invention, a method of manufacturing a switch comprises: forming at least two vertically extending vias in a wafer; filling the at least two vertically extending vias with a metal to form at least two vertically extending wires; and opening a void in the wafer from a bottom side such that at least one of the vertically extending wires is moveable within the void.

"In an aspect of the invention, a method of manufacturing a MEMS switch comprises: etching at least three vias from a top side of a wafer; filling the vias with a metal to form vertically arranged top side wires; depositing a dielectric material on the bottom side of the wafer; etching the dielectric material to form an opening therein, wherein remaining portions of the dielectric material protect edges of the wafer; and etching a bottom side of the wafer through the opening in the dielectric material to form a void which exposes at least one of the vertically arranged top side wires.

"In an aspect of the invention, a MEMS switch comprises: at least three vertically extending metal wires formed in a wafer; and a void formed in the wafer which accommodates at least one of the at least three vertically extending metal wires. The at least one of the at least three vertically extending metal wires is moveable within the void upon an application of a voltage.

"In another aspect of the invention, a design structure embodied in a machine readable medium for designing, manufacturing, or testing an integrated circuit is provided. The design structure comprises the structures and/or methods of the present invention."

URL and more information on this patent, see: Anderson, Felix P.; Cooney, III, Edward C.; McDevitt, Thomas L.; Stamper, Anthony K.. Vertical Integrated Circuit Switches, Design Structure and Methods of Fabricating Same. U.S. Patent Number 8791778, filed September 16, 2013, and published online on July 29, 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=8791778.PN.&OS=PN/8791778RS=PN/8791778

Keywords for this news article include: International Business Machines Corporation.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Journal of Engineering


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters