Temperature sensors are frequently provided in integrated circuits to detect when the operating temperature limits have been exceeded. Typical integrated circuit (IC) solutions for sensing temperature change use a semiconductor temperature sensor manufactured, entirely on the IC. Such ICs include transistors, bolometers and pyroelectrics. The integrated circuit sensor typically employs an integrated diode whose output characteristics are dependent upon temperature. The semiconductor temperature sensor can be a forward-biased pn junction diode or variations thereof as is known in the art, such as a diode connected npn or pnp bipolar transistor. Bolometers incorporating temperature sensors are well known devices for measuring radiation, and in these devices the temperature sensors are arranged to have temperatures dependent on the flux of incident radiation. Different types of bolometer are used for measuring different types of radiation in various environments; in fusion experiments, for example, bolometers are used to measure quantitatively the radiation and neutral particle emission from the plasma. The resistance temperature detector (RTD) takes advantage of the principal that the resistivity of metals is, to a small degree, dependent upon temperature. RTDs include all metals in the form of wire, thin/thick-films and foil, in which the change in metal resistance vs temperature produces a change in voltage drop, under constant current bias. Thermistors include hot-pressed and/or fired ceramics, with embedded electrical contact wires; the principle of operation is identical to that of RTDs. The thermistor is a temperature sensitive resistor and is generally composed of semiconductor materials. Thermocouples include metals, in the form of wires or thin-films, in which the junction formed between 2 dissimilar metals generates a temperature dependent voltage. The thermocouple method takes advantage of the fact that, when two wires composed of dissimilar metals are joined at the ends and one of the ends is heated, there is a continuous current generated which flows in the thermo-electric circuit. Thermocouples do not require electrical input to the TC junction but they do require an electrical input to maintain a reference junction. EMVs include devices such as metal coils and strips, and volumetric tube and bulb thermometers, in which expansion/contraction of the metal/fluid is used to measure temperature. Pyrometers which are sensitive to infrared, optical and acoustic wavelengths, convert the input wavelength to an optical or electronic output by means of an IC, RTD, thermistor or thermocouple.

Temperature sensors normally generate an output signal that increases with increasing temperature. A temperature sensor comprises a sensing element housed in an elongated sheath. The sensing element itself may be an electrical resistive element. The sensor is commonly installed in a thermowell to position the sensor element at a location at which the temperature reading is desired. Temperature sensors such as digital thermometers often measure temperature by exploiting the thermal-voltage characteristics of a diode. The temperature coefficient of a diode is the voltage drop across the diode as a finction of temperature while the diode is forward-biased by a constant current. The thin-film temperature sensor is a thin-film type sensor which comprises an alumina or silicon substrate and multiple layers laminated on the substrate by using the semiconductor micromachining technique. Known examples of a thermal type infrared sensor with such a structure include a micro-thermistor bolometer and a thin-film thermistor. Thermistor devices for temperature sensors are used in the measurement of temperatures in the range 400-1300.degree. C. and are used in the measurement of automotive exhaust gas temperatures, gas flame temperatures in gas water heaters and the like, and the temperatures of heating ovens. Digital temperature sensors are well known. Digital temperature sensors are typically used to generate a temperature reference for the circuits on the chip or other integrated chips. Digital temperature sensors, such as voltage reference circuits, generate a temperature output signal by normalizing a thermometer voltage to a reference voltage. The analog to digital converter of the digital temperature sensor measures the temperature dependent voltage ratiometrically relative to the reference voltage. It is also known to use capacitors as temperature sensors, where temperature changes lead to dimensional changes of the dielectric material separating the capacitor's electrodes, resulting in changes in capacitance which can be measured using a capacitance bridge. The thermal type infrared sensor is a non-contact type sensor that measures the surface temperature of hot objects and moving objects. An infrared detecting portion of the sensor is heated by the energy of infrared radiated from the object being measured and a change in electric resistance of a thermal sensitive resistor making up the infrared detecting portion of the sensor is detected as a temperature change, from which the surface temperature is determined. To measure temperature by means of infrared emission, thermal (infrared) radiation can be detected either by quantum detectors or by thermal detectors. Quantum detectors, such as photoresistors or photodiodes, require cryogenic cooling to measure relatively low temperatures with high accuracy. On the other hand, thermal detectors, while not as sensitive as quantum, may operate at normal room temperatures.

Temperature sensors are utilized in a wide variety of applications in which it is necessary to monitor the temperature within a space. Temperature sensors are incorporated in a number of electronic circuits for a variety of purposes. A large number of circuits and/or functional units in today's electronic devices are temperature sensitive and require accurate and reliable temperature information in order to take corrective action when the temperature becomes too high. In the computer and data processing industry there is an ever increasing demand for higher processing speeds and systems which are capable of performing multiple tasks in parallel. To increase processor performance, clock frequencies used by microprocessors, often referred to as CPUs, have increased. Also, as the number of circuits that can be used in a CPU has increased, the number of parallel operations has risen. As processor performance continues to increase, the result has been a larger number of circuits switching at faster rates. Higher frequencies and data throughput cause a processor to consume increased power and run at increased temperatures. Extreme temperatures can slow the speed of transistors that may cause some CPU activities to be incomplete at the end of a cycle. Dissipation by integrated circuits exceeding a safe temperature limit needs to be signaled so that the dissipation can be controlled. In addition, the operating temperature range for a particular electronic system may have to be limited. For integrated circuits such as processors heat sinks are provided to dissipate heat generated by the processor. Fans are typically utilized in conjunction with heat sinks to blow air on the fins of the heat sink to achieve greater cooling through convection. Temperature detectors have been used for monitoring the operating temperature of non-volatile EEPROM memories used in smartcards. Smartcards are plastics cards having an integrated circuit, such as a memory circuit or a microcontroller, embedded therein. These cards are increasing in popularity for a variety of applications, including credit cards, POS cards, telephone cards, access control cards, etc. Temperature sensors with a relatively high degree of accuracy are used in smart antenna systems for ground based applications (e.g., cellular antennas) and airborne applications (e.g., airplane or satellite antennas). Smart antenna systems, such as adaptive or phased array antennas, combine the outputs of multiple antenna elements with signal processing capabilities to transmit and/or receive communications signals. With temperature sensors, such antenna systems can vary the transmission or reception pattern of the communications signals in response to the signal environment to improve performance characteristics.

Temperature sensors are utilized to monitor a variety of automotive systems, including for example coolant temperature and exhaust gas temperature. These sensors typically utilize a wire-type thermistor which is generally soldered to hard-wired leads. As engine technology becomes increasingly more sophisticated, the number and variety of sensors used in controlling the engine has continued to climb. Modern automotive engines typically rely on numerous engine parameters for correct engine operation. Optimum engine parameters are generally stored in the memory of an engine controller. Typical engines may include many sensors used to provide information to the vehicle owner, operator, and service personnel and/or used to control the engine. Temperature sensors may be used to provide engine protection by quickly detecting adverse operating conditions which may indicate a fault or malfunction to reduce or eliminate any permanent engine damage. The engine control module (ECM) monitors the sensor inputs to detect conditions which may trigger a diagnostic code or fault which may be used by owners/operators and/or service and maintenance personnel to troubleshoot and repair the engine. High temperature resistance temperature detector (RTD) sensors are used in emission-control systems used with internal combustion engines because they can detect changes in temperature with time constants on the order of about 10 seconds or less as is required in that type of application. To measure temperatures up to about 1,000.degree. C., thermocouples that use platinum/platinum-rhodium or nickel/chromium-nickel have been used. Temperature sensors for use need to be accurate and reliable while operating in the harsh vehicle environment over a long period of time. Further, since there may be many sensor assemblies per vehicle, the cost of the sensors must be minimized.

Temperature sensors are also used in a variety of other applications. For instance, a temperature sensor has been used in petrochemical industry, process control industry, electrical, oil and gas exploration & mining industries whereas exact measurement of particular temperature has to be controlled for getting the desired products or composition. Temperature sensors are commonly utilized in cold rooms to monitor the temperature within the area to ensure that the temperature does not increase to a point where the goods may be at a risk of spoilage. In such applications, a separate temperature sensor is connected to an alarm system to provide for a warning if the temperature increases beyond a particular limit. Storage areas where products are stored which must be kept from freezing are required to have the temperature monitored to ensure that it does not fall below a level at which the products may freeze. Temperature sensors are also used in greenhouses to maintain the temperature within an acceptable growing range, while also ensuring that the temperature has not reached a level which would cause permanent damage to the crops. LIG thermometers are standard equipment at laboratories and surface weather stations. LIG thermometers have a fine glass bore and a fluid reservoir. Operation depends on the thermal expansion of the liquid contained in the glass envelope. The sensitivity of the LIG thermometer depends inversely on the diameter of the bore of the tube and on the relative expansion coefficients of the liquid and glass.