SOI for the Real World
Posted date : May 11, 2007

TI is using SOI in key high-voltage, high-current and high-frequency analog components.

The real world is analog. Things like temperature, sound, light, pressure, speed – for this analog data to be integrated into digital systems, it has to be converted. But because the requirements vary enormously among the different analog functions and various systems where they are used, TI’s development of analog technologies follows several distinct paths.

To that end, in 2003 TI introduced BiCOM3, the industry’s first complementary SiGe Bipolar process for ultra-high speed and precision analog applications for 5V. In 2006 a 36V BICOM3HV has been added. BICOM3(HV) is ideal for creating things like high-speed (operational) amplifiers (that boost the analog signal for more accurate conversion to digital), as well as analog-to-digital converters (ADC) and digital-to-analog converters (DAC).

Now in volume production for a wide range of applications such as hard disk drives (HDD), wireless infrastructure and measurement equipment, BiCOM3 processes leverage SOI and deep trench isolation.

© Hélène Hilaire / (Courtesy: Sony Computer Entertainment Inc.); Pavel Kapish, Bluestocking / FOTOLIA

Consider the hard disk drive

To better understand why SOI and deep trench isolation are key aspects of the BiCOM3 process, let’s consider the fast-growing HDD market. TI is the leader in servo drivers and pre-amps for HDDs; cost, size and performance are key.

In a disk drive, the analog signal picked-up by the read/write head needs to be amplified: this “signal conditioning” is the job of pre-amp chips. The boosted signal is then converted into a digital signal by the ADC chips. The digital data can now be processed by a microprocessor and DSP. Reading from a HDD, writing to it and the data conversion to/from digital are the domain for our SOI-based analog technologies.

Continuing with the HDD example: since package density of the magnetic domains on the disk gets higher, the signal/noise ratio gets worse. Low-noise, high-speed pre-amplifiers are needed to boost the signal to a level where ADCs can work.

Due to the small mechanical dimensions of the read head in HDDs, we need chips with small footprints. SOI and full dielectric trench isolation enable a denser layout, which reduces chip size significantly: that lowers our costs. Reduced chip size and lower parasitic capacitances translate into lower power consumption, reduced signal distortion and a higher frequency range.

In terms of reliability, the SOI plus trench isolation approach prevents latch-up. And because there is no leakage between components or circuits, the chips have a higher thermal stability, so they can be used in hot environments. These benefits from SOI and trench isolation are applicable across the entire analog chain. This reduces system thermal issues, increases long-term reliability and provides a key benefit for customers designing environmentally-friendly products.

(Source: Texas Instruments)

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