Metallic Coulomb blockade thermometry down to 10 mK and below

We present an improved nuclear refrigerator reaching 0.3 mK, aimed at microkelvin nanoelectronic experiments, and use it to investigate metallic Coulomb blockade thermometers (CBTs) with various resistances R. The high-R devices cool to slightly lower T, consistent with better isolation from the noise environment, and exhibit electron-phonon cooling ∝?T?(5) and a residual heat-leak of 40 aW. In contrast, the low-R CBTs display cooling with a clearly weaker T-dependence, deviating from the electron-phonon mechanism. The CBTs agree excellently with the refrigerator temperature above 20 mK and reach a minimum-T of 7.5 ± 0.2 mK.     

Highly reliable temperature sensor using rf-sputtered SiC thin film

A SiC thin-film thermistor for high-temperature use has been developed by using rf-sputtered SiC thin films. This thermistor can be used for industrial and consumer use within an operating temperature range of -100 to 450 degrees C. By using SiC thin films, the thermistor maintains high electrical stability. The resistance change is less than 3% after exposure to heat at 400 degrees C for 2000 h. In addition, the film growth technique made possible the production of a high-accuracy thermistor, i.e., thermistor coefficient < +/-0.5%, thermistor resistance < +/-1.5%.     

A monolithic silicon multi-sensor for measuring three-axis acceleration,pressure and temperature

A monolithic multi-sensor for small unmanned aerial vehicles is presented in the paper; it consists of a three-axis piezoresistive accelerometer, a piezoresistive absolute pressure sensor and a silicon thermistor temperature sensor. The accelerometer is designed with four silicon beams supporting the seismic mass and appropriate piezoresistors arrangement to detect three-axis acceleration and greatly reduce cross-axis sensitivities. For minimizing the effect of stress on the temperature sensor, the thermistor is designed along [100] and [010] crystal orientation. The multi-sensor is fabricated on SOI wafers by using MEMS bulk-micromachining technology. Some effective micromachining steps are applied in the fabrication. The two-step wet anisotropic etching process on the backside of the wafers can form the whole backside shape of the multi-sensor. The metal electrode sputtered on the Pyrex glass can avoid sticking between the Pyrex glass and the seismic mass in the process of anodic bonding. The die size of the multi-sensor is 4×6×0.9mm³. The measured results show that the multi-sensor is appropriate for its application field.     

Invited review article: A 10 mK scanning probe microscopy facility

We describe the design, development and performance of a scanning probe microscopy (SPM) facility operating at a base temperature of 10 mK in magnetic fields up to 15 T. The microscope is cooled by a custom designed, fully ultra-high vacuum (UHV) compatible dilution refrigerator (DR) and is capable of in situ tip and sample exchange. Subpicometer stability at the tip-sample junction is achieved through three independent vibration isolation stages and careful design of the dilution refrigerator. The system can be connected to, or disconnected from, a network of interconnected auxiliary UHV chambers, which include growth chambers for metal and semiconductor samples, a field-ion microscope for tip characterization, and a fully independent additional quick access low temperature scanning tunneling microscope (STM) and atomic force microscope (AFM) system. To characterize the system, we present the cooling performance of the DR, vibrational, tunneling current, and tip-sample displacement noise measurements. In addition, we show the spectral resolution capabilities with tunneling spectroscopy results obtained on an epitaxial graphene sample resolving the quantum Landau levels in a magnetic field, including the sublevels corresponding to the lifting of the electron spin and valley degeneracies.     

红外探测中潜艇冷热尾流的传热传质特性

本文采用有限体积法建立了1/72龙鲨Ⅱ号核潜艇的三维计算模型,结合动参考系、用户自定义函数和物性多项式函数等实现了高速旋转螺旋桨和海水温度密度分层的仿真。基于该模型,探讨了螺旋桨高速旋转、海水温度密度分层和高温热尾流喷射等因素对潜艇冷热尾流传热传质特性的影响,所得结论如下:高速旋转螺旋桨促使热尾流后向延迟距离增大、海表温差减小,忽略旋转时海表温差的绝对误差和相对误差分别为3.23mK和52.7%;水下航行潜艇扰动温度密度分层海水浮升形成冷尾流温差信号,与温度密度均匀海水相比,海表温变区域显著增大、尾流温差由6.13mK增大到84mK;通过海表上游冷尾流特征判断是否存在水下航行潜艇,若存在,再结合海表下游热尾流特征实现潜艇位置的精确反演。上述结论可为优化潜艇冷热尾流的数值仿真精度提供参考与借鉴。     

High-precision temperature control and stabilization using a cryocooler

We describe a method for precisely controlling temperature using a Gifford-McMahon (GM) cryocooler that involves inserting fiber-reinforced-plastic dampers into a conventional cryosystem. Temperature fluctuations in a GM cryocooler without a large heat bath or a stainless-steel damper at 4.2 K are typically of the order of 200 mK. It is particularly difficult to control the temperature of a GM cryocooler at low temperatures. The fiber-reinforced-plastic dampers enabled us to dramatically reduce temperature fluctuations at low temperatures. A standard deviation of the temperature fluctuations of 0.21 mK could be achieved when the temperature was controlled at 4.200?0 K using a feedback temperature control system with two heaters. Adding the dampers increased the minimum achievable temperature from 3.2 to 3.3 K. Precise temperature control between 4.200?0 and 300.000 K was attained using the GM cryocooler, and the standard deviation of the temperature fluctuations was less than 1.2 mK even at 300 K. This technique makes it possible to control and stabilize the temperature using a GM cryocooler.     

Ultra-sensitive thermal conductance measurement of one-dimensional nanostructures enhanced by differential bridge

Thermal conductivity of one-dimensional nanostructures, such as nanowires, nanotubes, and polymer chains, is of significant interest for understanding nanoscale thermal transport phenomena as well as for practical applications in nanoelectronics, energy conversion, and thermal management. Various techniques have been developed during the past decade for measuring this fundamental quantity at the individual nanostructure level. However, the sensitivity of these techniques is generally limited to 1 × 10(-9) W∕K, which is inadequate for small diameter nanostructures that potentially possess thermal conductance ranging between 10(-11) and 10(-10) W∕K. In this paper, we demonstrate an experimental technique which is capable of measuring thermal conductance of ～10(-11) W∕K. The improved sensitivity is achieved by using an on-chip Wheatstone bridge circuit that overcomes several instrumentation issues. It provides a more effective method of characterizing the thermal properties of smaller and less conductive one-dimensional nanostructures. The best sensitivity experimentally achieved experienced a noise equivalent temperature below 0.5 mK and a minimum conductance measurement of 1 × 10(-11) W∕K. Measuring the temperature fluctuation of both the four-point and bridge measurements over a 4 h time period shows a reduction in measured temperature fluctuation from 100 mK to 0.6 mK. Measurement of a 15 nm Ge nanowire and background conductance signal with no wire present demonstrates the increased sensitivity of the bridge method over the traditional four-point I-V measurement. This ultra-sensitive measurement platform allows for thermal measurements of materials at new size scales and will improve our understanding of thermal transport in nanoscale structures.     

DESIGN OF AN AUTOMATED FEEDBACK CONTROL COOLING SYSTEM FOR SWIR LINEAR IMAGE SENSOR APPLICATION

Our novel automated feedback temperature controlled cooling system consists of a temperature measurement circuit, a TE cooler, a thermistor, a microcontroller, and a digital-to-analog converter and PWM algorithms. The measurement accuracy of this temperature controlled TE system was better than 0.1°C and can be used for maintaining an instrument's isothermal applications. The experimental results of SWIR linear image shows that the temperature can be stably maintained at ?20°C, the dark output current can be reduced almost 80 mV (Integration time: 100 ms) and the SNR of pixel can be improved from 48 dB to 83 dB as well.     

Design and modeling of an intelligent temperature to frequency converter

This paper presents the development of an intelligent temperature to frequency converter to measure the temperature using a negative temperature coefficient (NTC) thermistor. The signal conditioning circuit (SCC) of the NTC thermistor is a modified timer circuit whose control voltage is generated by a difference amplifier. The thermistor SCC acts as a temperature to frequency converter and exhibits a moderate linear temperature-frequency characteristic over a range of 0–100 °C with a linearity error of ±3.5%. A multilayer perceptron (MLP) neural network with Levenberg–Marquardt (LM) algorithm is used for modeling and nonlinearity estimation of the converter. The LM algorithm effectively reduces the linearity error as compared to the Broyden–Fletcher–Goldfarb–Shanno (BFGS) and the scaled conjugate gradient (SCG) algorithms. Mean square error (MSE), regression coefficients, linearity, accuracy and dispersion spread are used to evaluate the performance of the proposed ANN-based modeling. The intelligence of the ANN-based modeling is embedded in a low cost microcontroller unit and the performance is experimentally verified on a prototype unit. The linearity error and sensitivity of the proposed unit are approximately ±0.35% and 5 kHz/°C respectively.     

Compact and accurate digital thermometer based on Anderson’s loop and Pt-100 sensor

A simple and practical digital thermometer with an accuracy better than 0.1°C over a near-room-temperature (from −10°C to 50°C) measurement range has been developed. The instrument is compact and battery operated and provides for both digital and analog outputs. A four-lead platinum thermal sensor, driven by a constant current loop, allows for accurate temperature readings with high immunity to the contact resistances and to their variations. A low-noise electronics allows for temperature measurements with a 1 mK resolution. By experimentally characterizing the non-linearity of the adopted Pt-100 sensor, a suitable readout correction table has been calculated in order to compensate for the sensor non-linear behavior. This compensating procedure allows for a wider (from −50°C to +200°C) and higher accuracy (0.05°C) measurement range. The ultimate accuracy was essentially limited by the accuracy of the temperature standard used for calibration.     

智能式热电阻校验仪的研制

本文介绍了一种以单片机为核心的智能式热电阻校验仪的硬件工作原理及其软件设计。该校验仪具有收发热电阻信号的双重功能，独到之处是可发出无源热电阻信号及对应的温度值。     

Use of quantum-point-contact high-electron-mobility-transistors for time domain multiplexing of large arrays of high impedance low temperature bolometers

The use of a multiplexing readout for an array of bolometers simplifies the electronics and wiring, so making the readout of large arrays of bolometers (>100) feasible. Here we describe a time domain multiplexing technique and its performance based on the use of quantum-point-contact high-electron-mobility-transistors as low temperature (to approximately 100 mK) switches for measuring high impedance (5...70 MOmega) resistances and sensors. The presented system is well matched to ground based millimetric astronomy demands.     

Voltage divider resistance for high-resolution of the thermistor temperature measurement

When measuring temperature with a voltage divider, and changing the variation of the thermistor resistance from the temperature to the voltage, the divider resistance greatly impacts the resolution of each ADC step. This work presents a method for determining the divider resistance to minimize the resolution’s maximum value in a given temperature range. Since the function of the resolution strongly depends on the derivative of the thermistor resistance, we also investigated the effect on the resolution when the derivative was calculated by forward and backward finite differences and the Stein–Hart calibration equation. The results showed that the resolution’s maximum calculated by the three methods had only a 5% difference, for the four types of commonly used NTC thermistors. Also, we demonstrated that the divider resistance which minimizes the interval resolution’s maximum can be determined by the thermistor resistance and its derivative at each end of the temperature range.     

Reduction of temperature fluctuation within low temperature region using a cryocooler

Modeling and experiments are performed to decrease temperature fluctuation generated by the periodic motion of the displacer in a Gifford-McMahon (GM) type cryocooler within the low-temperature region. The one-dimensional heat equation allows us to show that thermal diffusivity is an essential factor to achieve much smaller temperature fluctuation, and fiber-reinforced plastic (FRP) with low thermal diffusivity makes it possible to reduce the temperature fluctuation dramatically. Based on the model, experiments are performed to vary the thickness of two FRP dampers, on the cryohead of the cryocooler and on the sample stage. As a result, the FRP dampers enable us to achieve the temperature fluctuations of only 0.7 mK, corresponding to a standard deviation of 0.25 mK, when the sample stage is maintained at 4.2000 K, even if a GM cryocooler is utilized for cooling the temperature, which introduces an initial temperature fluctuation of 282 mK at the cryohead.     

Local variability in PTC thermistor grain boundary structures

Scanning electron microscopy-based conductive mode (CM) microscopy, using the remote electron beam-induced current configuration, was carried out on a positive temperature coefficient of resistance thermistor at temperatures below and above the Curie temperature, T(C). Below T(C), when the thermistor is in a low resistance state, no strong CM contrast was observed. Above T(C) the thermistor grain boundaries become highly resistive and significant CM contrast formed owing to three mechanisms: all of the areas that were studied showed resistive contrast, but in addition some grain boundaries showed additional contrast due to electron beam-induced current, the origin of which was consistent with the presence of a back-to-back Schottky barrier structure at the grain boundary. Other grain boundaries exhibited additional contrast owing to beta-conductivity, which suggests a slightly different n-i-n grain boundary structure at these interfaces. These results suggest that electrically active grain boundaries with different structures coexist within the thermistor.     

Construction of a dilution refrigerator cooled scanning force microscope

We present a scanning force microscope that operates in a dilution refrigerator at temperatures of about 100 mK. We use tuning fork sensors for scanning gate experiments on mesoscopic semiconductor nanostructures. Slip-stick motors allow sample coarse-positioning at base temperature. The construction, thermal anchoring, and a procedure to optimize the settings of the phase-locked loop that we use for sensor control are discussed in detail. We present low-temperature topographic and scanning gate images as examples of successful operation.     

厚膜一体化温湿度传感器中热敏材料的制备工艺及机理研究

概述了一体化温湿度传感器的特点及发展现状，对厚膜一体化温湿度传感器中热敏材料的设计、制备方法及特性进行了深入的研究，对实验结果进行了分析讨论。给出与一体化传感器中湿敏材料相匹配的负温度系数热敏材料的成分与阻温特性的关系，制备工艺对阻温特性及材料粒度、粒度均匀性的影响，同时，还给出了几组热敏材料的实验数据和用此材料制备的一体化厚膜温湿度传感器的特性曲线。     

High resolution ac calorimeter for organic liquids

A calorimeter has been developed for organic liquids which utilizes the ac heat capacity technique. It can measure heat capacity changes of 1 part in 10(4) with a temperature resolution better than 1 mK from room temperature to 200 degrees C. This calorimeter has been used to study the smectic A to nematic phase transition in a series of homologous liquid crystals.     

Piezoelectric rotator for studying quantum effects in semiconductor nanostructures at high magnetic fields and low temperatures

We report the design and development of a piezoelectric sample rotation system, and its integration into an Oxford Instruments Kelvinox 100 dilution refrigerator, for orientation-dependent studies of quantum transport in semiconductor nanodevices at millikelvin temperatures in magnetic fields up to 10 T. Our apparatus allows for continuous in situ rotation of a device through >100° in two possible configurations. The first enables rotation of the field within the plane of the device, and the second allows the field to be rotated from in-plane to perpendicular to the device plane. An integrated angle sensor coupled with a closed-loop feedback system allows the device orientation to be known to within ±0.03° while maintaining the sample temperature below 100 mK.     

PTC延时控制及其在电子镇流器中的应用

ＰＴＣ热敏元件通常是以钛酸钡为基的半导体制成，本文介绍了ＰＴＣ元件的温度主要是由器件消耗的电功率所控制的场合。例如，过流保护，延时控制（预热功能）以及在电子镇流器中的应用。