Microwave Engineering Europe - October 2007 - (Page 14)

14 CMOS RF Si-on-sapphire goes mainstream By John Boyd, Semiconductor Insights esigners developing mobile handsets must accommodate ever-moredemanding user requirements, including increased functionality, lighter weight, lower cost and longer battery life. Additionally, state-of-the-art handsets continue to shift to higher RF frequencies, as a result of overcrowding of existing unlicensed bands as well as the need to deliver the higher data rates demanded by applications such as video streaming. Advanced handsets can operate on a number of frequency bands. The RF switching needed to provide the integration and connectivity for these multiple bands to the antenna is testing the limits of conventional technology. The antenna switch module (ASM) is usually the tallest device in the radio section of the handset, and it draws a fair amount of current. Technologies that reduce the form factor and power consumption of the ASM are therefore of great interest. An increasingly popular alternative for front-end switching is RF CMOS. Leadingedge CMOS technology has enabled the fabrication of ICs with mind-boggling device densities and performance, providing RF designers with the manufacturing advantages of CMOS (integration, power, cost, manufacturability and scalability) and the improved RF performance that process scaling can bring. Though the silicon substrate in a bulk device is excellent for the fabrication of active devices, it is a compromise material that provides neither perfect isolation nor conduction. Silicon can limit RF performance by capacitive coupling of the RF devices to the resistive substrate. That leads to dissipation of RF energy, poor-quality-factor passives, crosstalk, and injection of thermal noise back into the circuit. An alternative CMOS technology, siliconon-insulator (SOI), consists of a layered silicon-insulator-silicon substrate. On SOIbased devices, the silicon junction sits on the insulating layer (usually silicon oxide) and enables complete dielectric isolation of devices. Additionally, bonded SOI substrates may be used to combine high-resistivity substrates with standard IC processing. The insulator used in an SOI device is typically silicon dioxide or, less commonly, sapphire. Traditionally, sapphire was used for radiation- D Figure 1: NMOS transistor in the CMOS logic area of the PE42612. sensitive applications (aerospace and military), while silicon oxide was preferred for improved performance and diminished shortchannel effects in microelectronic devices. SOI devices generally have lower parasitic capacitance than bulk silicon devices and can reduce power consumption at matched performance. A further beneﬁt of SOI is latchup resistance due to complete isolation of the n- and p- well structures. SOI substrates are compatible with almost all conventional wafer-fabrication processes and can be implemented without signiﬁcant retooling of an existing factory. Furthermore, SOI substrates are readily available at 300-mm diameters. Silicon-on-sapphire (SOS) has for years been recognized as a technically superior semiconductor vehicle and the ultimate form of SOI, offering silicon on a perfect isolator with no parasitic capacitance at high-frequency operation. But price, yield, availability and process issues have limited SOS to military and aerospace projects. In the past few years, SOS has been signiﬁcantly improved, as demonstrated by Peregrine Semiconductor’s process achievements, which addressed yield problems and enabled more cost-effective commercialization of the technology. Peregrine’s technology enables the type of RF solutions required for multiband ASMs. In April 2004, Peregrine announced a broad licensing agreement with Oki Electric Industry Co. Ltd. that transferred Peregrine’s 0.5-µm UTSi SOS to Oki’s Hachioji, Japan, Figure 2: Die photograph of Peregrine Semiconductor’s PE42612 SP4T RF switch. The image was taken though the backside of the transparent sapphire substrate. Microwave Engineering Europe ● October 2007 ● www.mwee.com 014-016_MWEE.indd 14 20/09/07 13:01:58 http://www.mwee.com

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Microwave Engineering Europe - October 2007 Contents Comment News CMOS RF: Si-On-Sapphire Goes Mainstream Cover Feature: New Data Protection Concept for UHF RFID Tags CMOS RF: RF Design Team Touts CMOS Spin for 3G PAs Wireless HID – Are You Following the Standard to Another “Average” Product Development? Phase Optimisation of the RF Front-End Direct Synthesis of UWB-WiMedia Signal Generation 4G Chips to Target 700 MHz Applications Femtocells Mobilize to Fight Wi-Fi in the Home Products Product Feature: AXIEM Pioneers the Future of EM Technology Calendar

Microwave Engineering Europe - October 2007

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