Precision Temperature Measurement

 Herbert Chelner, CEO and Chief Scientist

Dr. Robert A. Mueller, President and General Manager

Abstract

Micron Instruments is best known for its world-class semiconductor strain gages and pressure transducers. Micron also sells an extremely small and highly accurate semiconductor temperature sensing element made from the same materials but doped differently than the strain gage. As such, the semiconductor temperature sensing element offers many of the compelling benefits as the semiconductor strain gage.

The ST-037-022-5000N is a Silicon Semiconductor "N"-doped bulk type Temperature Sensing Element that develops a large resistive change with temperature. This thermo-resistive device is etched from a solid piece of doped material and has a minimum of molecular slippages and/or dislocations resulting in a highly reliable device. When used as recommended, a signal resolvable to 0.001° F is possible.

Semiconductor Strain and Temperature Gages

Semiconductor strain gages were discovered during the transistor era and became commercially available early in the 1950's. These gages may be homogeneous or diffused or silicon on sapphire (SoS) deposited. Diffused gages have a variety of problems that limit useful life and affect performance.  SoS deposited gages have a much lower gage factor and are less corrosion resistant.

There are two main elements from which semiconductor gages are made. These elements are Geranium and Silicon and they can be P or N doped. At Micron Instruments, the P doped (Boron) Silicon gage is selected for the basic strain sensor, and the N doped Silicon is used for the temperature sensing element. Silicon gages have been proven to be more stable, more sensitive, and more corrosion resistant than Geranium gages.

Micron Instruments Miniature N-doped Silicon Semiconductor Temperature sensing element

Micron’s homogeneous silicon temperature sensing element, the ST-037-022-5000N, is a thermo-resistive device that has an ultra-fast response time. Further, the ST-037-022-5000N’s silicon composition offers high reliability, corrosion resistance, and a high measurement output. This N doped crystal is only 0.037” long, 0.004” wide, and 0.0004” thick (0.9mm by 0.1mm by 0.01 mm). This small mass allows the sensing element to have a very fast response to temperature even in a poor thermal transmitter and heat capacity fluid like air.

The ST-037-022-5000N has a very large change in resistance of 20 ohms per °F (36 ohms per °C) about ambient. With a repeatable resistance versus temperature curve, represented by a second order polynomial, it can be used with a microprocessor to read temperature accurately, or used in a resistive bridge configuration, and produce a linear change with temperature of as much as 10 millivolts per degree F (18 millivolts per degree C) between -65°F and 185°F (-80°C and 75°C).

Micron Temp Sensor Figure1

Figure 1.

The ST-037-022-5000N has a gage factor of less than 10. When bonded to a material that has an expansion of ten micro inches per inch, the ST-037-022-5000N will change the linear output by about 2.0%, or two degrees per hundred degrees. The output will still be repeatable and, if in a bridge circuit, will still be linear assuming the modulus of elasticity is relatively linear.

Micron Temp Sensor Figure 2

 Figure 2.

Precision Temperature Measurement Applications

Like the thermistor, the ST-037-022-5000N is a device that changes its electrical resistance with temperature. However, unlike typical thermistors, the silicon semiconductor temperature (SST) device is capable of large changes in resistance for a small change in temperature – high output.

In applications requiring very fast response time, the small mass of the ST-037-022-5000N makes it an alternative, for some applications, to other Resistance Temperature Devices (RTDs).

The ST-037-022-5000N is an excellent choice for the manufacturing of heat loss flow meters, measuring hot spots in circuit board or the temperature of components during operation, as a feedback control for heaters or coolers such as air conditioners or temperature chambers and etc.

A recommended Wheatstone bridge completion circuit for the ST-037-022-5000N is shown below in Figure 3.

Micron Temp Sensor Figure 3

Figure 3.

Wireless Measurement

With an ambient resistance of 5,000 Ω, the ST-037-022-5000N is an excellent choice for use in wireless systems, requiring minimum energy to activate data acquisition and communication for passive RFID transceivers.

Gaging Services

Applying a gage as small as the ST-037-022-5000N can be challenging. If you have a precise temperature measurement application and would like assistance gaging and verifying some prototype articles, contact us to get started.

Contact Us.

Micron Instruments has already worked with innovative companies on optimal selection, placement, and processing of semiconductor strain gages and temperature devices for high frequency, high pressure, and high-temperature applications. If you’d like to discuss your application or design, please contact us for a free, confidential consultation either by email using our Contact Us Form or phone (805-522-4676)

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