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Dual Action RF-MEMS Switch Suits System-on-Chip Integration |
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Geneva, July 21, 2003 - STMicroelectronics (NYSE:STM), one of the world's leading semiconductor manufacturers, has released details of an innovative technology that uses MEMS (Micro-Electro-Mechanical Systems) techniques to integrate high performance radio-frequency (RF) switches into circuits fabricated using standard CMOS technology. The new RF switch promises to enhance the performance of mobile phones and similar portable terminals where efficient RF switching is required to minimize power consumption and thereby extend battery life. To allow portable terminals to fully adapt to their environment by switching from one standard to another or by efficiently controlling the transmission power, equipment manufacturers are increasingly demanding more flexible RF chips with more efficient on-chip switching capabilities. Semiconductor devices are widely used as RF switches in portable applications but are less attractive, in principle, than MEMS-based switches, which can offer better performance in terms of isolation, insertion loss and linearity. However, although the benefits of RF-MEMS switches are established in numerous aerospace and telecommunication applications, their feasibility in very high volume markets such as mobile phone terminals depends critically on the ability to integrate them into low-cost System-on-Chip (SoC) devices. The "Above IC" microswitch solution, jointly developed by ST and its long-term research partner CEA-LETI at ST's Crolles1 facility, meets the four key criteria of high reliability, low power consumption, low actuation voltage and compatibility with SoC fabrication techniques. To demonstrate the integration of the new RF-MEMS switch in a SoC design, prototypes were fabricated using an industrial BiCMOS technology for the driver circuit used for the thermal actuation and electrostatic clamping. The actual MEMS switch is fabricated above the chip, i.e. after all the standard CMOS process stages have been completed, and require no special bonding techniques. "This achievement is an excellent example of how ST, working with its research partners, is a world leader in developing innovative extensions to the standard CMOS platform", said Herve Mingam, Program Director, Central R&D. "This new technology promises to be an exciting addition to our comprehensive portfolio of System-on-Chip technologies." Following the successful fabrication and characterization of the first prototypes, ST and CEA-LETI are now working to optimize the electrostatic hold function, develop wafer-level packaging and further increase cost-effectiveness by reducing the number of masks required. The new RF-MEMS technology was developed and demonstrated at ST's Crolles1 facility at Crolles, near Grenoble, France. Established in 1992, Crolles1 is a fully integrated facility with R&D, pilot production and volume manufacturing all closely coupled to ensure optimum efficiency. Crolles1 hosts joint teams between ST, France Telecom R&D and CEA-LETI, working on advanced technologies to prepare future CMOS platforms and since 1992 has included a joint R&D team from ST and Philips Semiconductors. ST, Motorola and Philips have more recently joined their R&D forces, forming the "Crolles 2 Alliance" to jointly develop these future generations of CMOS technology from 90nm to 32nm nodes and to build a jointly owned Crolles2 300mm pilot line that will reproduce the successful R&D-production coupling developed in Crolles1. TSMC is partner to the Crolles2 Alliance, in a common effort to align the Design Rules of the digital core process to ensure design portability and the access to the IPs developed on this common platform. About STMicroelectronics STMicroelectronics is a global leader in developing and delivering semiconductor solutions across the spectrum of microelectronics applications. An unrivalled combination of silicon and system expertise, manufacturing strength, Intellectual Property (IP) portfolio and strategic partners positions the Company at the forefront of System-on-Chip (SoC) technology and its products play a key role in enabling today's convergence markets. The Company's shares are traded on the New York Stock Exchange, on Euronext Paris and on the Milan Stock Exchange. In 2002, the Company's net revenues were $6.32 billion and net earnings were $429.4 million. Further information on ST can be found at http://www.st.com. Technical Notes · The moving element in the switch consists of a tiny beam (400 x 50µm) of silicon nitride, clamped at each end. The beam, which includes titanium nitride heating resistors, electrostatic holding electrodes and an aluminum block at each end, is initially separated from the RF signal line that runs underneath it by a 3µm air gap. When a low voltage (2V) is applied to the heating resistors, the different thermal expansions of aluminum and silicon nitride cause the beam to deform ("bimorph effect") until it make mechanical contact with a gold bump on the RF line, closing the switch. · Once the switch has been turned ON, a voltage is applied to the holding electrodes, producing an electrostatic force that retains the beam in position, allowing the heating current to be turned off. In this way, the new structure combines the benefits of the low voltage power supply and high reliability brought by thermal actuation with the low power consumption of the electrostatic clamping. · For activation, the switch requires a 20mA current under 2V for around 200µs, resulting in activation energy of 8µJ. For the first prototypes, the voltage required to achieve electrostatic hold was 15V and with improved stress control for the beam material this is expected to be reduced to 10V. In terms of reliability, more than 109 switching cycles were demonstrated without any failure or contact degradation, while the RF characterizations yielded excellent insertion loss (0.18dB) and isolation (57dB) at the 2GHz frequency of interest in mobile phone applications. |
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