The Promise of High Resistivity SOI for Wireless Communications Systems
Posted date : Oct 31, 2007

ST reports on highly integrated SRAM and RF on 300mm wafers. Yield matches bulk with improved FOM.

Wireless communications systems may soon replace personal computers as a key driver of volume manufacturing.

A full CMOS 65nm Partially Depleted Low Power (LP) SOI technology has been developed at STMicroelectronics on high resistivity (HR) ( 1kOhm-cm) 300mm SOI wafers provided by Soitec. This latest work is the first to prove that 300mm HR SOI can match bulk yield, with improved figures of merit (FOM) of both digital and RF circuits, for high-volume wireless applications

Figure 1. 3-stage 80 GHz Low Noise Amplifier - 65nm Low Power SOI (Courtesy: STMicroelectronics)

Figure 1. 3-stage 80 GHz Low Noise Amplifier - 65nm Low Power SOI (Courtesy: STMicroelectronics)

HR SOI: better RF, even without thick copper

This HR SOI substrate helps increase the integration of passive components by area saving for given quality factors, without a very thick copper back-end process. The functional RF circuits are state of the art with low noise and high gain, even in the very high frequency range.

An HR substrate can’t be used on bulk due to latch-up. With low resistivity substrates, parasitic capacitances and the attenuation constant of propagation lines degrade high-frequency performance, especially for mm-wave circuits above 60GHz.

HR SOI: Lower-power or higher-speed SRAM with same yield as bulk

Limited battery life makes power dissipation the main issue for wireless portable systems.

Compared to a similar design in bulk, the 65nm HR SOI on 300mm wafers gave us:

  • A 25% power reduction for similar frequency or a 40% higher maximum operating frequency for a 2Mb SRAM.
  • Similar standby leakage at low drain voltage and at 25°C for SRAM, so that leakage can be managed by design solutions, as for bulk. Elsewhere, body contacted devices can be used to switch power off.
  • The same yield as bulk when specific process optimizations are done.

HR SOI: a good candidate for SOC

Thin SOI advanced technologies with a high resistivity substrate are consequently very good candidates to integrate RF and digital circuits in the same chip, as RF performance as well as a lower power and higher speed can be reached with a full standard SOI CMOS process.

References: “80 GHz Low Noise Amplifiers in 65nm CMOS SOI”, Baudouin Martineau et al, ESSCIRC 2007 “Integrated Inductors in HR SOI CMOS technologies: on the economic advantage of SOI technologies for the integration of RF applications”, Frederic Gianesello et al, IEEE Int. SOI Conference 2007.

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