Tag Archives: Temperature

How does temperature affect component life?

Change in temperature affects the speed, power and reliability of electronic components and systems. Variation of temperature affects the speed performance, because material characteristics depend on temperature. These dependencies may be normal or reversed based on the type of the semiconductor material. Additionally, these dependencies change with technology scaling, and manufacturers counteract by introducing new processing materials, using metal gates and high-K dielectrics.

For example, temperature influences various performance functions in a MOSFET. These include the carrier density, energy band gap, carrier diffusion, mobility, current density, velocity saturation, leakage current, threshold voltage, electro-migration and interconnect resistance.

Temperature dependence of carrier density for a doped material occurs in three distinct regions. The material has just enough latent energy in the ionization region to push a few of the dopant carriers into the conduction band. When the material is in the extrinsic region, which is the desired region of operation, the carrier concentration remains flat over a wide range of temperatures.

This region has all the dopant carriers energized into the conduction band, and there is minimum generation of additional thermal carriers. However, as the temperature increases, the extrinsic region converts into the intrinsic region, with the number of thermally generated carriers exceeding the number of donor carriers. Typically, the intrinsic carrier concentration in a material is generally much smaller than the concentration of dopant carriers at room temperatures. However, intrinsic carrier concentration is highly temperature dependent and once the number of thermally generated carriers exceeds the number of dopant-generated carriers, the potential for thermal variation problems increases substantially.

At low temperatures, lattice vibrations in the material are small and electrons move more slowly. Thus, ion impurity forces dominate the limit to mobility. As temperature decreases, it takes less time for an electron to pass an impurity ion, which means the mobility decreases. The reverse is true when temperature rises; the carrier’s thermal velocity increases, consequently decreasing the impact of interface charges.

With an increase in temperature, the kinetic energy of particles within the material also increases, effectively increasing the diffusion component of the total current. Two parameters, mobility and carrier density affect the total current through the material. While the carrier density remains nearly fixed with temperature over the extrinsic range or the intended range of operation, the mobility term or the drift component of the total current actually decreases with an increase in temperature.

Since the temperature dependencies of diffusion and drift currents are of opposing nature, the net current change depends on the applied electric field and affects the threshold voltage and leakage current of the MOSFET. Manufacturers typically design the MOSFET such that its threshold voltage decreases linearly with increasing temperature. However, the leakage current doubles for every 10°C rise on temperature.

The resulting change in device current based on temperature can have devastating effects leading to timing failures, systems exceeding power or energy budgets and errors in communication between cores. This is more commonly known as reverse temperature dependence, which is the increase of electrical conduction with increase in temperature, first discovered by C. Park of Motorola, in 1995.

Measuring Temperature Remotely

How to Measure Temperature Remotely

In hostile atmospheres like toxic zones, very high temperature areas or remote locations, where objects are not amenable to direct temperature measurements, remote measurement techniques are deployed. In such applications, remote temperature measuring techniques are resorted to, and devices used include Infrared or Laser Thermometers as described below.

Infrared Thermometers or Laser Thermometers

These devices sense the thermal radiation, also called Blackbody Radiation, emitted by all bodies, and the emission depends on the physical temperature of the object whose temperature is to be sensed. Laser Thermometers, Non-contact Thermometers or Temperature Guns are names of variants that use lasers to direct the thermometer towards the object.

In these devices, a lens helps the thermal energy converge onto a detector, which in turn, generates an electrical signal, and drives a display after temperature compensation. The devices produce fairly accurate results and have a fast response, unlike direct temperature sensing, which is difficult, slow to respond to or not accurate enough. Induction heating, firefighting applications, cloud detection, monitoring of ovens or heaters are some typical examples of remote measurement of temperature. Other examples from the industry include hot chambers for equipment calibration and control, monitoring of manufacturing processes, and so on.

These devices are commercially available in a wide range of configurations, such as those designed for use in fixed locations, portable or handheld applications. The specifications, among others, mention the range of temperatures that the specific design is intended for, together with the level of accuracy (say, measurement uncertainty of ± 2°C).

For such devices, the most important specification is the DISTANCE-TO-SPOT RATIO (D:S) where D is the object’s distance from the device, and S denotes the diameter of the area whose temperature is to be measured. This implies that a measurement by the device concerned provides the average temperature over an area having a diameter S with the object placed at a distance D away from the device.

Some thermometers are available with a settable emissivity to adapt to the type of surface whose temperature is being measured. These sensors can thus be used for measuring the temperature of shiny as well as dull surfaces. Even thermometers without settable emissivity can be used for shiny objects by fixing a dull tape on the surface, but the error would be larger.

Commercially Available Types of Thermometers:

• Spot Infrared Thermometer or Infrared Pyrometer, for measurement of temperature at a spot on the object’s body

• Infrared Scanning Systems, for scanning large areas. This functionality is often realized by using a spot thermometer that aims at a rotating mirror, such as piles of material along a conveyor belt, cloth or paper sheets, etc. However, this cannot be termed a thermometer in the true sense.

• Infrared Thermal Imaging Cameras or Infrared Cameras are the ones that generate a thermogram, or an image in two dimensions, by plotting the temperature at many points along a larger surface. The temperatures sensed at various points are converted to pixels, and an image is created. As opposed to the types described above, these are primarily dependent on processor- and software-for functioning. These devices find use in perimeter monitoring by military or security personnel, and monitoring for safety and efficiency.