New technology offers designers an electronically adjustable micro-resistor

Montreal, Canada – Microbridge Technologies Inc., a privately held technology company announced the introduction of the Rejustor the world's first electronically precision-adjustable passive micro-resistor device.

The Rejustor is a passive, VLSI and MEMS compatible micro-resistor. It is non-volatile, and re-adjustable many times, bidirectionally, to very high precision, using only electrical signals. Rejustors can also be temperature coefficient matched with other Rejustors, again using only electrical signals. All adjustments can be carried out at low voltage and low current before and/or after packaging or even in-circuit after years of operation.

“With the Rejustor, for the first time circuit designers have at their disposal a low cost electronically controlled high precision bidirectional adjustment capability for in-circuit automation of resistive trimming in electronics,” said Mike Foster, CEO of Microbridge Technologies.

“Pairs of Rejustor devices can be resistance matched to typically better than 0.005% and, in a world's first, their temperature coefficient of resistance can be adjusted to match another Rejustor to better than 2 ppm/&degK, or intentionally adjusted to a precise mismatch in TCR to help temperature compensate electronic circuitry,” said Les Landsberger, Microbridge's chief technology officer.

Rejustors are CMOS and BiCMOS process compatible, so as well as soon being available as discrete devices, they can be incorporated into analog, mixed-signal and systems-on-chip integrated circuit designs. Rejustors are particularly interesting for RF applications as passive adjustable resistors with low capacitance and excellent high-frequency performance.

“The combination of precision resistance adjustment and TCR matching or controlled TCR mismatch provided by the Rejustor takes analog and sensor design beyond today's capabilities to the next stage of precision performance over wide temperature ranges,” said Nick Tasker, vice president of business development at Microbridge. “A new generation of high performance semiconductor integrated circuit devices is now possible.”

Rejustor devices will be demonstrated for the first time in public at the Microbridge Technologies booth at IEEE MEMS 2004, January 25-29 in Maastricht, Netherlands.

Montreal, Canada – Microbridge Technologies Inc., a specialist in micro-systems technology, says its new polysilicon resistor dubbed the Rejustor is the industry's first electronically precision-adjustable micro-resistor. This device provides high-precision resistive trimming without requiring manual or mechanical adjustments.

Typically, resistive adjustment is performed via mechanical trimpots that require manual adjustment, and digital potentiometers that offer limited resistance values or limited resolution. Laser trimming technology is also used, but it only allows for trimming in one direction before packaging. This new technology is capable of trimming using only electrical signals, as well as before or after packaging, or in-circuit during calibration.

Other advantages cited include bidirectional adjustment, which may improve manufacturing yields, as well as the capability to do multiple adjustments. It may also be temperature coefficient matched with other Rejustors, again before or after packaging.

Another important point to note is the trimming algorithms for the Rejustor are compatible with standard production test equipment without any modifications to implement the software.

While circuit designers may be skeptical, the new technology can provide resistive trimming electronically, and do it at a lower cost and in a smaller form factor than other trimming devices such as mechanical trimpots and digital potentiometers, claims Nick Tasker, vice president of business development for Microbridge.

“We understand there is a fairly significant mindset that has to change to adopt this technology. A designer sitting down to design a circuit has to now look at the idea of being able to trim electrically,” Tasker explained. “Anywhere you need to change or adjust a resistive value, you can benefit by doing it electrically rather than in the conventional way.”

Compatible with passive, MEMS and VLSI (CMOS, BiCMOS) technologies, the new device can be used as a discrete component or integrated with semiconductors or MEMS devices in a variety of applications such as voltage references and regulators, op amp gain and offset, sensor conditioning, ac-to-dc converter control and feedback system control. They can be incorporated into analog, mixed-signal and system-on-chip (SoC) IC designs.

The simplest way to implement the technology is as a discrete component. In comparison with traditional methods of trimming, engineers gain by eliminating the need to manually trim mechanical trimpots or use laser trimming, which requires an investment in capital equipment. Plus, laser trimming only allows one time adjustment before packaging and trimming in one direction.

Offering an integrated solution with the Rejustor is a bit more complicated and requires a very close relationship between Microbridge and the customer to develop design rules and the integrated component design. This may be a major hurdle to overcome for companies that don't have in-house MEMS expertise.

Preliminary specs include:

  • A resistance range of approximately 50 ohms to several Mohms
  • Bidirectional adjustment over a typical 30% range
  • Resistance matching of 0.01% to 0.001% with matching resistance adjustment resolutions (0.01% to 0.001%)
  • Power rating is initially 1 mW
  • Adjustment life demonstrated up to hundreds of cycles
  • Adjustable at low voltage (2-12 V) and low current (2-5 mA)

While the micro-resistor technology holds promise, packaging may be a key roadblock to bringing the technology into the commercial, high-volume production arena, and presents a major hurdle in downsizing the device.

Tasker says packaging is a big challenge because the company is still limited to some degree by the processes available for wafer level packaging, and is forcing the device to be larger than what it needs to be. At this time, Microbridge is working with several companies with MEMS packaging expertise to develop wafer level packaging for its new devices.

The company announced last week the selection of X-FAB Semiconductor Foundries of Germany as a foundry partner for initial manufacturing of the Rejustor. The good news is that X-FAB has expertise in both CMOS and MEMS manufacturing.

Tasker recommends that engineers try out the technology by using the company's demo kit. By doing this, designers will start to more clearly associate the technology for potential applications in their own domains, he said.

After roughly 18 months of development work, Microbridge is ready to offer samples to the industry. A limited range of devices, based on resistance values, will be available in second quarter 2004. Initially, the devices will be available in 8-pin and 16-pin DIP packages. Evaluation kits will also be available in second quarter.

Call Nick Tasker at (514) 938-8089, ext. 228 for more information.

Call (514) 938-8089

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