Integrated Temperature Sensor Research Articles

Self-Powered Wireless Sensor for Air Temperature and Velocity Measurements With Energy Harvesting Capability

Air temperature and velocity measurements are important parameters in many applications. A self-powered sensor placed in a duct and powered by an electromechanical generator scavenging energy from the airflow has been designed and tested. It periodically transmits the measured air temperature and velocity to a receiving unit. The system basically consists of two macroblocks, respectively: the self-power wireless sensor and the receiving unit. The self-powered sensor has a section devoted to the energy harvesting, exploiting the movement of an airscrew shaft keyed to a dc motor. The self-powered sensor adopts integrated devices in low-power technology, including a microcontroller, an integrated temperature sensor, and a radio-frequency transmitter at 433 MHz. The data transmission is realized in Manchester encoding, with amplitude-shift-keying modulation at 433 MHz, allowing covering a distance between the sensor and the reader on the order of 4-5 m, depending on the power supplied in transmission. The air velocity is measured through the rotor frequency of the electromechanical generator, whereas, for the temperature, a commercial low-power sensor is used. An experimental system has been designed and fabricated, demonstrating that the airflow harvester can power the self-powered wireless sensor permitting air temperature and velocity measurements. The system can be used for real-time monitoring of temperature and velocity. The sensor module placed into the duct does not require any batteries.

Experimental study of heat-treated thin film Ti/Pt heater and temperature sensor properties on a Si microfluidic platform

Design, fabrication and characterization of thin film Ti/Pt heaters and integrated temperature sensors on a Si microfluidic platform are presented. Ti/Pt heaters and sensors provide controlled heating of microchannels realized on the opposite side of the Si platform. Ti/Pt heaters and sensors were fabricated simultaneously by a dc sputtering method and a lift-off process. Thermal annealing of deposited Ti/Pt layers in the temperature range of 300–700 °C was investigated revealing a strong impact on the Ti/Pt resistivity and, consequently, on the final resistance of fabricated heaters and sensors. Furthermore, it was determined that the temperature coefficient of resistance (TCR) for Ti/Pt temperature sensors and the heater increased with the annealing temperature. Microstructural analysis of deposited and annealed Ti/Pt layers carried out by AES and AFM revealed that recrystallization followed by a grain growth process of heat-treated Ti/Pt layers started at around 500 °C and correlated well with the behavior of electrical properties, but not with the TCR behavior of annealed layers. To reduce the heat losses of the heated Si platform, the heater and temperature sensors were covered hermetically by anodically bonded Pyrex glass with a prefabricated insulating cavity. According to this approach the power consumption was reduced by more than 25% due to the improved thermal insulation. Additional insulation steps implemented during thermal characterization of the assembled microfluidic platform further reduced the power consumption, but also increased the time response of the microfluidic reactor.

인듐틴옥사이드와 몰리브데늄을 이용한 외부 기준 저항이 필요 없는 온도센서

Display quality depends on panel temperatures. To compensate it, temperature sensor was integrated on the panel. The conventional temperature sensor integrated on the panel needs external reference resistor. Since the resistance of external resistor can vary according to the variation of the environment temperature, the conventional temperature sensor can make error in temperature sensing. The environmental temperatures can change by the back light unit, driving circuits or chips. In this paper, we proposed a integrated temperature sensor on display panel which does not need external reference resister. Instead of external reference resistor, we used two materials which have different temperature coefficient in resistivity. They are connected serially and the output voltage was measured at the point of connection with the applied voltage to both ends. The proposed sensor was fabricated with indium tin oxide(ITO), and Mo metal electrode temperature sensor which were connected serially. We verified the temperature senor by the measurements of sensitivity, lineality, hysteresis, repeatability, stability, and accuracy.

Accurate operation of a CMOS integrated temperature sensor

A high-accuracy temperature sensor is designed by applying the temperature characteristics of substrate bipolar transistor in CMOS technology. Initial accuracy of the temperature sensor can be improved by chopper amplifiers and dynamic element matching. Using these two methods, the circuit realization of reference voltage is also described. Simulation results show that the inaccuracy is within×0.4°C from −40 to +100°C. Experimental results, obtained from circuits fabricated in 0.5μm CMOS process, indicate that the sensor is inaccurate within×0.7°C from −40 to +100°C. The power dissipation is 0.35mW and the chip area is 889μm×620μm. Compared with previously reported work, the temperature sensor in the paper has lower inaccuracy without calibration.

Non-linear thermal modeling of DMOS transistor and validation using electrical measurements and FEM simulations

The relevance of thermally non-linear silicon material models for transient thermal FEM simulations of smart power switches (SPS) is proved by a power silicon test device consisting of two power transistors and eleven integrated temperature sensors distributed over the silicon die. The test device is heated up by turning on an integrated power transistor in short-circuit for several milliseconds at two different initial temperatures. These thermal events correspond to a real situation that can occur in the application. The power dissipation in the power transistor is calculated from the measured source current and drain-source voltage, and subsequently used as an input to the FEM simulation. The temperature change on the test chip is measured by the integrated temperature sensors. An FEM model of the test chip encapsulated in a plastic package has been built in the FlexPDE simulator. The emphasis is put on the macroscopic modeling of the power transistor where an electro-thermal approach is reduced to a purely thermal one. Finally, the thermal events are simulated using FEM and compared to the temperature measurements. The results have shown that our modeling approach including non-linear properties of silicon can be used to investigate the thermal transients in SPS devices with high accuracy.

Development of SAW-based multi-gas sensor for simultaneous detection of CO 2 and NO 2

A 440 MHz wireless and passive surface acoustic wave (SAW)-based multi-gas sensor integrated with a temperature sensor was developed on a 41° YX LiNbO 3 piezoelectric substrate for the simultaneous detection of CO 2, NO 2, and temperature. The developed sensor was composed of a SAW reflective delay lines structured by an interdigital transducer (IDT), ten reflectors, a CO 2 sensitive film (Teflon AF 2400), and a NO 2 sensitive film (indium tin oxide). Teflon AF 2400 was used for the CO 2 sensitive film because it provides a high CO 2 solubility, with good permeability and selectivity. For the NO 2 sensitive film, indium tin oxide (ITO) was used. Coupling of mode (COM) modeling was conducted to determine the optimal device parameters prior to fabrication. Using the parameters determined by the simulation results, the device was fabricated and then wirelessly measured using a network analyzer. The measured reflective coefficient S 11 in the time domain showed high signal/noise (S/N) ratio, small signal attenuation, and few spurious peaks. The time positions of the reflection peaks were well matched with the predicted values from the simulation. High sensitivity and selectivity were observed at each target gas testing. The obtained sensitivity was 2.12°/ppm for CO 2 and 51.5°/ppm for NO 2, respectively. With the integrated temperature sensor, temperature compensation was also performed during gas sensitivity evaluation process.

Analytical Investigation of Fuel Cells by Using <i>In Situ </i>and <i>Ex Situ </i> Diagnostic Methods

The study of the behaviour of fuel cells by using various in-situ and ex-situ diagnostic methods is a main topic at the German Aerospace Center (DLR). The degradation of cell components of polymer electrolyte fuel cells (PEFC, DMFC) and of solid oxide fuel cells (SOFC) are of special interest. For this purpose physical and electrochemical methods are used individually as well as in combination. In addition to routinely applied electrochemical methods different methods for locally resolved current density measurements by means of segmented cell technology and integrated temperature sensors have been developed. The latest development with segmented bipolar plates based on printed circuit boards (PCB) is used both in single PEFC cells and stacks. Furthermore, a measuring system for segmented SOFC cells has been developed allowing for the spatially resolved characterisation of cells in terms of current density/voltage characteristics, impedance spectroscopy data, operating temperature and gas composition. The paper summarises the capabilities at DLR with respect to the analysis of fuel cells’ behaviour and gives examples of analytical studies to discuss the potentials and limitations of the diagnostic methodology that is applied.

Design of CMOS integrated temperature sensor based on chopping and dynamic element matching

Design of CMOS integrated temperature sensor based on chopping and dynamic element matching

A microchip integrated temperature sensor with RF communication channel and on-chip antenna

A wireless CMOS temperature sensor chip performing an embedded RF antenna is presented. The RF carrier is produced by a three-stage ring oscillator that also acts as sensing element exploiting a linear dependence of oscillation frequency on temperature. The antenna is a square loop fabricated using the top metal layer provided by the 0.35 μm CMOS technology. Oscillation frequency shifts due to bias voltage fluctuations are circumvented by using a mathematical technique.The microchip provides an RF power level of -45 dBm at a distance of 1 m. The average power consumption is about 50 μW.

Thermally mediated control of liquid microdroplets at a bifurcation

The ability to precisely control the motion of droplets is essential in droplet-based microfluidics. It serves as the basis for various droplet-based devices. This paper presents a thermal control technique for microdroplets at a bifurcation. Control was achieved using an integrated microheater that simultaneously induces a reduction in fluidic resistance and thermocapillarity. The temperature of the heater was monitored by an integrated temperature sensor. At a bifurcation with symmetric branches, a droplet can be split into two daughter droplets of controllable sizes or entirely switched into a desired branch. The physics of this phenomenon was investigated with the help of a numerical model. Splitting and switching were demonstrated within an operational temperature range 25–38 °C. The relatively low operational temperature range allows this technique to be used for droplets containing biological samples. The present control concept is not limited to bifurcations, but can be employed in other geometries.

Basic investigation of microtemperature sensor by means of a novel transmission-line technique using a temperature-sensitive Li–Zn–Cu ferrite substrate

The polycrystalline Mn-substituted Li–Zn–Cu ferrite exhibits a very strong temperature dependence of magnetic properties, high natural resonance frequency, and high resistivity. The authors carried out the basic investigations of the temperature sensor using this new temperature-sensitive ferrite. As the first step, the temperature-sensitive LC resonance circuit using the Li–Zn–Cu ferrite chip inductor was fabricated, and the temperature dependence of its input impedance was evaluated. The resonance frequency was decreased linearly with a large temperature coefficient. Furthermore, it was also found that the input impedance in a constant frequency operation indicated extremely temperature dependence. In order to integrate and miniaturize the temperature sensing device, a possibility of the integrated temperature-sensitive LC circuit by means of the transmission-line technique was investigated. For our motivation, the monolithic integrated temperature sensor using spiral strip-line with Li–Zn–Cu ferrite substrates, which has the temperature dependent magnetic property, was simulated by the electromagnetic field and the equivalent circuit analysis. It was clarified that the monolithic sensor exhibited remarkable temperature dependent input impedance as well as the temperature-sensitive LC resonance circuit.

Technical Note: Construction of a Low-Cost Black Globe Thermometer

An economical self-contained globe thermometer was developed for use in field applications. The instrument uses a miniature integral temperature sensor and datalogger in place of a separate sensor and external datalogger. The performance of the miniature sensor/logger units was shown to be satisfactory for use in globe thermometers. Calibration of the units showed a linear behavior with standard errors ranging from 0.02C to 0.04C for the span of 15C to 90C. The integral sensor/logger performed as well as the thermistor/external logger combination and can be fabricated at a low cost.

Design and characterization of a humidity sensor realized in LTCC-technology

A new type of integrated temperature and humidity sensor applying Low Temperature Cofired Ceramics technology (LTCC) has been developed and characterized. The proposed device is based on the detection of the difference of thermal conductivity between water vapor and dry air. In this approach, sensing elements are implemented using heated metal film resistors (Pt-elements), where one is exposed to the humid environment that causes the sensor element to cool down with increased humidity, while the other one is sealed from the environment. LTCC-tapes are used for the formation of caps as well are acting as substrate. Sensor design is based on finite element analyses (FEA) where the critical design parameters have been analyzed with regard to the performance characteristic of the device.

Diode temperature sensor array for measuring micro-scale surface temperatures with high resolution

A diode temperature sensor array (DTSA) was developed for measuring the temperature distribution on a small surface with high resolution. The DTSA consisted of an array of 32 × 32 diodes (1024 diodes) for temperature detection in an 8 mm × 8 mm surface area and was fabricated using the very large scale integration (VLSI) technique. A flip chip packaging technique was used for electrical connections between the pads of the DTSA chip and the PCB (printed circuits board). Circuits for scanning temperatures at 1024 detection points were also developed. Each diode of the DTSA exhibited a strong linear relation between the forward voltage drop and the temperature. The DTSA may be applied to various micro-thermal systems that require highly integrated temperature sensors in a small area.

Focus on lasers and optics

Focus on lasers and optics

Enthalpy of Vaporization and Vapor Pressures: An Inexpensive Apparatus

An inexpensive apparatus is described for the determination of the vapor pressure of a liquid as a function of temperature for the purpose of calculating enthalpy changes of vaporization. The solid-state pressure transducer is linear above 100 torr, is useful in the range -40 to 85 °C, and is calibrated using pure water. The experimental enthalpies of vaporization for ten solvents are within ca. 0 to 13% of literature values. Two different versions of the static vapor pressure apparatus are described. Also described are a simple air thermostat and an inexpensive temperature controller (±0.1 K) based on an integrated temperature sensor. The measurement time is under three hours.

CMOS‐compatible fabrication of porous silicon gas sensors and their readout electronics on the same chip

AbstractIn this work, integration on the same chip of porous silicon gas sensors along with their driving/readout electronic circuits by using an industrial microelectronic process is demonstrated. To ensure maximum compatibility, the porous silicon formation is performed after the integrated circuit fabrication flow is completed. The chip contains three CMOS operational amplifiers, a band‐gap voltage reference, an integrated temperature sensor and several porous silicon‐based NO2 sensors. The simultaneous functionality of the electronics and the sensor is demonstrated by using various circuit blocks to implement a simple driving/readout electronic interface for the sensor. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A novel technique for the measurement of liquid viscosity

A novel technique for the measurement of liquid viscosity is presented. In this technique, a disk was driven by a constant speed dc shunt motor in the test liquid. The change in the motor current measured the viscosity. The change in motor current was measured using an instrumentation amplifier and the viscosity of the liquid was measured in terms of output voltage. The temperature of the liquid was controlled using a peltier cooler/heater and was measured using an AD590 two-terminal integrated circuit temperature sensor. The viscosity of vegetable oils (groundnut, palm, sunflower, coconut) in the temperature range from 20 °C to 60 °C were determined. The results thus found were similar to the results obtained from a Redwood viscometer. This technique is useful to measure viscosity of liquids.

Investigation of two-phase transport phenomena in microchannels using a microfabricated experimental structure

Microchannels (0.05–1 mm) improve gas routing in proton exchange membrane fuel cells, but add to the complexities of water management. This work microfabricates experimental structures with distributed water injection as well as with heating and temperature sensing capabilities to study water formation and transport. The samples feature optical access to allow visualization and distributed thermometry for investigation of two-phase flow transport phenomena in the microchannels. The temperature evolution along the channel is observed that the temperature downstream of the distributed water injection decreases as the pressure drop increases. As the water injection rate is lower than 200 μl/min, there exists a turning point where temperature increases as the pressure drop increases further. These micromachined structures with integrated temperature sensors and heaters are key to the experimental investigation as well as visualization of two-phase flow and water transport phenomena in microchannels for fuel cell applications.

An integrated pressure and temperature sensor based on nanocrystalline porous silicon

A novel integrated pressure and temperature sensor based on nanocrystalline porous silicon is reported here with a view to develop a smart pressure sensor. A twin MEMS porous silicon/silicon heterojunction structure is designed, fabricated and tested for the integrated pressure and temperature sensor. Pressure and temperature sensitivities have been studied at different porosities of the porous silicon membrane. The optimized porosity is observed to be around 55% for which the pressure sensitivity is about three times and temperature sensitivity is comparable to that of other types of integrated silicon sensors. The design of the integrated sensor has been done by maintaining isotherm characteristics of pressure and temperature sensors and eliminating the cross-coupling effect at the same time.