This Small Business Innovation Research Phase-II project is aimed at developing Micro Metal Sphere (MMS) fabrication technology for Radio-Frequency (RF) Micro-Electro-Mechanical-System (MEMS) switch. The target applications are high-bandwidth RF switches and digitally-tunable RF modules that can be used in wireless communication systems including cell phone. The MMS technology is distinguished from conventional cantilever or bridge type MEMS switches in that it does not have suspended element and no restoring force is involved in the switch actuation. In conventional MEMS switches, the restoring force is often not able to overcome interfacial forces over time and causes the infamous stiction that leads to permanent failure. Since the MMS switch is designed to switch with free body, it does not suffer from mechanical wear and possibly free from stiction. In addition, the MMS technology can provide an extremely cost effective packaging solution replacing commonly used labor intensive and costly wafer level packaging technology. Since the MMS technology is integration-friendly with conventional silicon CMOS technology, it can be placed on top of any CMOS IC. Therefore, anticipated benefit with the MMS technology extends to size reduction. Also the MMS technology is expected to lower the activation voltage below 10V.
Nano Liquid Devices (NLD) is the first U.S. company invented and developed RF-MMS process and cost effective packaging technologies that will enable mobile phone makers to design smaller, lower-cost smart phones, entry-level handsets and other mobile devices, which will accelerate the convergence of cell phones and computing for the next wave of mobile innovations. NLD's technology will enable lower-cost smart phones, which will complement and replace notebook PCs among mobile business people and students who access data and communications anywhere for work, study, social networking, and entertainment. About 1.5 billion cell phones will be produced in 2011, of which 67% will be multiband handsets, so the global impact will be enormous. NLD's RF-MMS technology will enable faster, better cell phone communications integrating voice, text and video for the average user worldwide.
In this third six months period of SBIR Ph-II, the prototype of the Micro Metal Sphere (MMS) RF switch was fabricated and characterized. The target applications of MMS RF switch are high-bandwidth RF switches and digitally tunable RF modules that can be used in wireless communication systems including cell phones A tunable module that can cover ultra wideband spectrum has a particular importance as it can contribute to increase the efficiency of radio spectrum in wireless communication. The basic working principle and structure of MMS RF switch are schematically illustrated in the Image 1. An MMS RF switch can be fabricated on the top of the top of the conventional CMOS IC as shown in the left. There are two driving electrodes (C1 and C2) and three RF nodes (D0, D1, D2) as shown in the right-hand side of the Image 1. When the driving electrode C1 is activated (by applying voltage), the MMS moves to the left and connects D0 and D1. Then the incoming RF signal from D0 is relayed to the output path D1. To make a path from D0 to D2, the driving electrode C2 is activated. The fabrication method of an MMS is illustrated in the Image 2. AuSn alloy is patterned by lift-off process and reflowed with proprietary annealing technology. The resulting MMS shape is shown in the SEM image. The functional diagram in conjunction with CMOS decoder and driver is shown in the Image 3. In this period of SBIR Ph-II, a prototype of MMS RF switch was fabricated and characterized. Image 4 shows the top and cross sectional schematics in the left and the actual device SEM image on the right. Shown are RF nodes D0, D1, and D2 in the SEM image. The measured RF characteristics, the insertion loss and the isolation, are shown in the Image 5. The insertion loss at 10GHz is around 0.6dB and isolation (in between D1 and D2) is around 30dB which significantly surpass those of the conventional RF switches being used in cell phones today. In the final period of the project, a tunable capacitor and inductor modules will be developed . To make a tunable inductor, as shown in the left-hand side of the Image 6, MMS RF switches S1, S2, and S3 are connected in parallel to the inductor elements L1, L2, and L3, respectively. If S1 is turned on, inductor L1 is by-passed and the total inductance between node A and B is L2 + L3 since S2 and S3 are turned off, Similarly, tunable capacitor can be made as shown in the right-hand side of the Image 6.