Electronic Design

SiGe BiCMOS Process Optimized For Cost-Sensitive RF Markets

In an effort to gain a competitive edge in the cost-sensitive wireless communications arena, STMicroelectronics has added silicon-germanium (SiGe) biCMOS to its arsenal of process technologies. The company has optimized its SiGe biCMOS process to produce RF chips that can address the needs of current and future generations of cell phones and other wireless gadgets. To guarantee capacity, the new process will be available from the maker's multiple fabs around the world. Production will start early next year.

To get the desired speed, this process implements Ge-ion implantation at high doses. Trench isolation techniques ensure that the noise factor of the heterojunction bipolar transistor (HBT) is substantially reduced. Also, nonselective epitaxial methods let the developers keep the manufacturing cost low. In fact, the SiGe biCMOS is compatible with the standard biCMOS process, says Nick Smears, marketing manager at STMicroelectronics.

The SiGe biCMOS additionally offers high-quality passives, including spiral inductors, to permit high levels of integration. An optional vertically isolated pnp is available. While the capacitors are derived using metal-insulator-metal (MIM) techniques, the polysilicon layers provide high-value resistors. The spiral inductors offer a quality factor (Q) of about 17 at 2 GHz.

Initially, the SiGe biCMOS will be implemented in a 0.35-µm lithography, which will create HBTs with a cutoff frequency (fT) of 45 GHz and a maximum oscillation frequency (fMAX) of 60 GHz. The trench isolation will hold the minimum noise figure to 0.8 dB at 2 GHz. The breakdown voltages of these HBTs are 3.6 and 5.0 V, according to STMicroelectronics.

The 0.35-µm SiGe biCMOS process was qualified last year. Several samples have been produced to demonstrate the technology. It will be exploited to produce both custom and standard RF chips, Smears notes. A custom transceiver for cellular applications is even in the process of being transferred to production. Though details were unavailable, it's expected to go into production in the first quarter of 2002. A Bluetooth transceiver is in development as well.

The supplier has also developed several standard RF transistors for low-noise amplifiers, prepower amplifiers, and similar functions. Called START, for STMicroelectronics Advanced RF Transistors, these faster high-performance discretes are slated for volume production in the second quarter of next year.

Meanwhile, efforts are under way to migrate to 0.25 µm in 2002, with an fT of 70 GHz and breakdown voltages of 2.8 and 5.0 V. STMicroelectronics hopes to qualify the 0.25-µm SiGe biCMOS process by the end of the year.

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