Thermistors are thermally sensitive resistors, which measure change in temperature with the change in resistance. In the case of negative temperature coefficient (NTC) thermistors, the resistance decreases as the temperature increases. However, traditional manufacturing techniques, which develop ceramic-based NTC thermistors, suffer from disadvantages such as change of resistance in humid environment and nonlinear resistance versus temperature characteristic over their operational temperature range. The solution is the use of linearization circuit or limiting their use over a smaller temperature range to minimize nonlinearity.

Palo Alto, CA-based AdSem Inc. has reportedly developed the worldís smallest germanium (Ge) NTC thermistor, which has a size of 150 micrometers. Interestingly, Michael Kozhukh, president, AdSem Inc., tells Sensor Technology, "When compared to companies that have been producing ceramic NTC thermistors with the same technology for years, AdSem Inc. has developed a novel technology for high-temperature semiconductor NTC thermistors and started their production. As a resultant of our years of expertise in this field, we have been able develop silicon (Si) and germanium (Ge) NTC thermistors, based on proprietary, patent-pending technology, that provide a plethora of advantages."

Si and Ge high-temperature NTC thermistors have better performance and are more cost effective than the typical ceramic NTC thermistor. They have higher sensitivity, higher operational temperature, wider temperature range of interchangeability; their resistance-temperature dependence is universal, they can be produced with smaller sizes, they donít interact chemically with moisture; they can be packaged at semiconductor packaging factories in high volumes with high productivity.

There are numerous industrial applications where ceramic NTC thermistors are currently employed for temperatures between minus 50 degrees C and plus 250 degrees C. AdSem's Si and Ge NTC thermistors can be used for all these applications providing higher thermo sensitivity, interchangeability in wider temperature range, smaller size, universal resistance-temperature dependence, lower cost compared to ceramic NTC thermistors. In addition, AdSemís silicon NTC thermistors are a suitable replacement in many applications for low-sensitive platinum RTD and thermocouples that operate between 250 degrees C and 500 degrees C. Small, high-sensitive Ge NTC thermistors can be employed for temperature measurements of internal organs of the human body. This provides a unique tool for development of new medical technologies and for improvement of existing techniques. Another suitable large-scale application for AdSem's high-sensitive semiconductor NTC thermistors is temperature measurements in system-in-package ICs, where small size, resistance-temperature (R-T) universality and compatibility with clean semiconductor fab environment are critical requirements.

AdSemís technology allows production of cryogenic Ge thermistors that operate down to 10 mK, have wider operational temperature range and higher interchangeability than any existing cryogenic temperature sensors. Highly sensitive Ge and Si radio frequency (RF) bolometers and large surface infrared (IR) bolometers can be also produced with AdSem's high temperature and cryogenic NTC thermistor technologies.

Currently, Adsem produces and sells Si and Ge NTC thermistors for any temperature between 10 mK and 500 degrees C. The most popular applications are different high-temperature measurements. The company expects their high-temperature semiconductor NTC thermistors to replace ceramic NTC thermistors. In the future, AdSem Inc. aims to develop novel NTC and PTC semiconductor thermistors with extended upper temperature range of 1000 degrees C. Kozhukh says, "These developments depend on speed of our growth, but for sure, it will happen in a few years because of obvious technical and price advantage of our Si and Ge high-temperature NTC thermistors in comparison with ceramic NTC thermistors."

Kozhukh adds, "We are a young company and as any company at this stage we are looking for ways to optimize a road to success. We have plans for large-scale production of diverse semiconductor thermistor products, we are working on further extension of operating temperature range of semiconductor thermistors, on development and production of multifunctional sensors based on our technology, on development of cost effective universal electronics for our sensors. We are open to any collaboration that will be beneficial for realization of these plans. There is a lot of work that has to be done, and right collaborators will help us and will share with us both the work and success."

Interestingly, sensitivity to cost is the biggest driver for sensor industry and development of new sensing techniques augments significant performance and cost benefits, and can open up new applications, which would eventually displace existing technologies.

Details: Michael Kozhukh, President, AdSem Inc., Palo Alto, CA. Phone: 650-852-0309. Fax: 650-852-0309. E-mail:

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