Current Issue An Independent Journal Dedicated to the Advancement of Chip - Scale Electronics July 2001 Email the editor

Steve Berry and Sandra Winkler Contributing Editors

Although radio frequency (RF) IC packages typically are very low I/O, such packages pose a number of challenges due to their speed and performance requirements.

The acronym "RF" loosely refers to an alternating current signal with a frequency between 300 MHz and 300 GHz. Any device that carries RF signals is called an RF device.

Encoded Pulses

In today's use of RF signals for the transmission of encoded digital data streams, the RF signal is rarely sent as a continuous signal, but is instead sent as a series of encoded pulses.

A good, clean pulse has a quick rise and fall time (quick relative to the receiver's response time) and a stable frequency, phase and amplitude. Noise and jitter are problems for RF chips, because they reduce the receiver's ability to decode the signal.

Information is encoded on an RF signal by rapid changes to the frequency, phase or amplitude. Noise can mask the changes and prevent the receiver from properly decoding the information.

The amplifiers in the RF chain are primary sources of internal noise; however, external noise often forces designers to impose band-width limits. Wider bandwidths cause more noise to enter the amplifier. Designers often employ filters to limit the noise entering systems from external sources.

SiGe/SOI Devices

Thermal issues are another problem for RF devices. High-frequency semiconductor materials often run very hot. This heat can lead to noise and reduced life. Several companies are working with silicon germanium (SiGe) and silicon on insulator (SOI) to combat this problem.

Silicon on insulator results in a 20 percent performance improvement and a 35 to 70 percent power reduction. Silicon germanium offers a high transistor speed with high linearity and a low noise figure, plus low power consumption-trading excess speed for lower operating power, and integrating silicon-based technology at higher performance while using existing CMOS manufacturing processes.

Many companies offer a variety of IC packages for the RF market. The following present just a very small sampling of the available RF packages:

• Intarsia Corp., Fremont, Calif., has developed a miniature low noise amplifier (LNA) module designed for high-performance wireless and RF applications. The module was developed using Intarsia's PassPort design palette for advanced thin film on glass microcircuits. The PHEMT LNA module is offered in a 4 x 4 x 1.2 mm surface-mount direct module attach (DMA) package and a face-up orientation for COB.

  The device includes all necessary biasing and matching circuits. The drop-in module is optimized for low noise figure (NF), exhibiting 1.1 to 0.8 dB NF over the 1.5 to 2.7 GHz frequency range. This module can therefore be used across a range of different or multiband RF front-end applications, such as GPS receivers, PCS and DCS base stations, and 2.4 GHz ISM designs.

• SyChip, a Lucent Technologies venture in Warren, N.J., designs and markets modules for wireless Internet appliances, based on micro-system integration tech-nology (MSIT) developed at Bell Labs over the past 15 years. SyChip targets semiconductor segments that are difficult or too expensive to integrate monolithically (RF passives, embedded memory). SyChip integrates the baseband, memory and RF sections into a chip-scale module. Its micro-system integration technology is composed of three key elements:

  • High-Q RF passive circuits in proprietary silicon substrates

  • Known-good die (KGD) and chip-on-chip (CoC) technologies

  • Flip-chip assembly processes

• Murata Manufacturing Co. Ltd., Japan, began shipping engineering samples of a small Bluetooth radio frequency (RF) module in July 2000. The RF module is an IC with RF analog elements, including an RF transceiver LSI, baluns, filters, and condensers. The module is only 6 mm x 8 mm, a reduction from the previous module size of 10 mm x 14 mm. i