Suppression of negative temperature coefficient of resistance of multiwalled nanotube/silicone rubber composite through segregated conductive network and its application to laser-printing fusing element

Negative temperature coefficient of resistance of a material can be a disadvantage in high temperature applications, causing a system to be thermally unstable as the temperature increases. We investigate the concept of excluded volume to suppress the negative temperature coefficient of resistance of a multi-walled carbon nanotube/silicone rubber composite. When micro- or nano-silica particles are incorporated to realize the segregated conductive network, the resistance-temperature dependence of the composite is suppressed in both the conductive polymer composite itself and a fuser unit for printers having the carbon nanotube composite as heating layer. It is believed that the effect of mechanical reinforcement and suppression in thermal expansion by the secondary particles are essential for suppressing the temperature dependence of resistance. This investigation on the excluded volume can be interpreted to offer a new perspective on nanomaterial-based thermistor technology.     

Variations of temperature coefficient and noise in thin Al and Al/Si resistors subjected to high current density

Electromigration (EM) in thin Al and Al/Si resistors was investigated by measuring the effect of the stress on the resistance, the temperature coefficientα, the low-frequency noise spectrum (20 mHz-1 Hz) and, for some Al samples, on the residual resistance atT = 11 K. It was found that the temperature coefficient variations versus the stress time have a different behavior for Al and Al/Si, that is an oscillation in the first part of the life of the sample and decreases in the last one, in the first case, whereas, in the second, only the oscillation was detected. This behavior, observed for the first time, has been modeled by means of the Mayadas theory, by supposing a Gaussian distribution of the reflection coefficient for electrons at the grain boundaries. The measurement of the residual resistance also supports the hypothesis that the behavior ofa andR _o (the resistance value at 273 K) is mainly due to the modification of the grain-boundary structure and cannot be explained by taking in account only the variation of the residual resistivity. Besides, the noise measurements give a further proof that the origin of the 1/fg spectra in thin films subjected to high current density must be ascribed to phenomena occurring at the grain-boundaries which are correlated to the phenomena causing temperature coefficient variations. This work was supported by the Progetto Finalizzato MADESS, CNR, Italy.     

Fabrication of amorphous ni- si films with small temperature coefficient of resistance by new flash evaporating method

Utilizing a heat treatment processes, Ni-Si thin films which have various resistivity and various and/or small temperature coefficients of resistance (TCR) can be fabricated by new flash evaporating equipment assembled in our laboratory. In relation to the increase of Si content in the film, the TCR of the as-deposited film increases negatively. By using heat treatment to stabilize it, the film's resistance decreases and its TCR shifts in a positive direction. These trends become more marked if the heat treatment is performed at high temperature for longer durations. Under optimal heat treatment conditions, samples with a range of resistivity from 250 to 3500 Μ Ω · cm and a small TCR can be obtained. By using Auger electron spectroscopy, we also clarify the composition change of the film's depth direction fabricated by this method is more uniform than that of direct evaporating method.     

A resistorless CMOS bandgap reference with low temperature coefficient and high PSRR

A novel bandgap reference (BGR) with low temperature and supply voltage sensitivity without any resistor, which is compatible with standard CMOS process, is presented in this article. The proposed BGR utilises a differential amplifier with an offset voltage proportional to absolute temperature to compensate the temperature drift of emitter–base voltage. Besides, a self-biased current source with feedback is used to provide the bias current of the BGR core for reducing current mirror errors dependent on supply voltage and temperature further. Verification results of the proposed BGR implemented with 0.35?µm CMOS process demonstrate that a temperature coefficient of 10.2?ppm/°C is realised with temperature ranging from ?40°C to 140°C, and a power supply rejection ratio of 58?dB is achieved with a maximum supply current of 27?µA. The active area of the presented BGR is 160?×?140?µm².     

氧压对ZnO薄膜电阻温度系数的影响

采用脉冲激光沉积(PLD)技术,在不同氧气氛下,在Si(lll)衬底上生长了ZnO薄膜,使用X线衍射仪分析了ZnO薄膜的结晶质量.计算了不同氧气氛下生长的ZnO薄膜的电阻温度系数(TCR)值,发现随着氧分压降低,ZnO薄膜的TCR值增大;ZnO薄膜的TCR值最高可达-8%/K.这为研究ZnO薄膜的导电特性提供了新的途径,开辟了ZnO薄膜在室温非制冷红外微测辐射热计材料中的应用潜力.     

The temperature mobility degradation influence on the zero temperature coefficient of partially and fully depleted SOI MOSFETs

The zero temperature coefficient (ZTC) is investigated experimentally in partially (PD) and fully depleted (FD) SOI MOSFET fabricated in a 0.13 μm SOI CMOS technology. A simple model to study the behavior of the gate voltage at ZTC (V_ZTC) is proposed in the linear and the saturation region. The influence of the temperature mobility degradation on V_ZTC is analyzed for PD and FD devices. Experimental results show that the temperature mobility degradation is larger in FD than in PD devices, which is responsible for the V_ZTC decrement observed in FD instead of the increment observed in PD devices when the temperature increases. The analysis takes into account temperature dependence model parameters such as threshold voltage and mobility. The analytical predictions are in very close agreement with experimental results in spite of the simplification used for the V_ZTC model as a function of temperature in the linear and the saturation region.     

Effect of nitridation on the electrical properties of W:Ti resistors

The electrical properties of tungsten-titanium (W:Ti) thin film resistors sputtered in an argon-nitrogen atmosphere were investigated. The resistivity ρ and the thermal coefficient of resistivity α were calculated as a function of film thickness and nitrogen content. A bulk resistivity of 70±4 μΩ-cm and the mean free path λ_o), of 0.8±0.1 μm were obtained for samples sputtered without nitrogen. The authors believe this to be the first report for the value of the λ_o in sputtered W:Ti. By appropriately controlling the nitrogen content during sputtering, it is possible to vary the value of α from positive to negative. It was found that α decreases with the nitrogen content and is zero at 0.5% N₂. This added degree of freedom in controlling α allows the integrated circuit designer to compensate the thermal effects within a circuit by customizing the resistor parameters without significant layout modifications.     

HgCdTe探测器Pt电阻测温分析

研究了PV型HgCdTe探测器在1.319 μm连续激光辐照下的温升效应。根据探测器的分层结构及测温Pt电阻的位置(冷面上),推断Pt电阻测得的温度并不直接反映HgCdTe芯片的温度,而是比芯片温度低很多。实验测量了Pt电阻的温升,数值模拟了Pt电阻温度随时间的变化以及探测器各层结构的温升情况,理论分析结果与实验结果相一致。     

温度系数连续可调的带隙基准源电路设计

为了对薄膜晶体管液晶显示器(TFT-LCD)驱动芯片的驱动电压进行温度补偿以改善TFT-LCD的性能,本文基于标准CMOS(3.3V)的chrt35rf 0.35$m工艺,设计了一款温度系数可连续调节的带隙基准电压源,其中包括核心电路、运算放大器电路和启动电路3个子模块。该电路使用MOS晶体管作为可变电阻,通过调节MOS栅极电压控制MOS漏源等效电阻的连续可变,进而改变电路中的电阻比值,实现带隙基准源的温度系数连续可调。使用Cadence的Spectre仿真器进行仿真,结果表明,在-25~125℃的工作温度范围内,带隙基准源电路的输出电压的正温度系数可连续调节范围为156.6~2 545.0ppm/℃,输出电压的负温度系数的连续变化范围为156.6~1 337.7ppm/℃,输出基准电压变化为0.95~2.67V,低频时基准电压的电源抑制比达到73.13dB。该电路实现了基准电压从负温度系数向正温度系数的连续可调节,且调节范围较大。     

基于负温度系数的多晶硅电阻电热激励/压阻检测微桥谐振器的新型红外探测器

报道了一种基于负电阻温度系数的多晶硅电阻电热激励/压阻检测SiO 2/Si3N4/SixNy微桥谐振器的新型红外探测器.微桥谐振器吸收的红外辐射引起微桥温度升高,激励电阻和检测电桥的阻值减小,使得恒定激励电压作用下激励电阻的静态功率和惠斯登电桥的焦耳热增加,等效于增加了辐射在微桥谐振器上的红外辐射.初步的实验证实了该方案的可行性.     

粉末环氧包封料对高压高阻电阻器的影响

研究了液体环氧、粉末环氧包封高压高阻电阻器后,电阻器主要电性能的变化。根据使用需要模拟实际,将这种电阻器再灌封在回扫变压器(FBT)环氧料中,研究电阻器的性能变化。确定了粉末环氧包封的可行性。试验表明：粉末环氧包封层适应FBT灌封环氧的收缩应力。高压高阻电阻器采用粉末环氧包封工艺还可提高生产效率和包封外观的一致性。     

Non-stoichiometry in SnTe thin films and temperature instabilities of thermoelectric properties

The temperature dependences of the Seebeck coefficient and the electrical conductivity for (0 0 1)KCl/SnTe monocrystalline thin films with thicknesses d=20–600 nm were obtained in the range of 80–300 K. In contrast with SnTe bulk crystals, these dependences exhibited anomalies (plateaus, steps, bends). It is suggested that as temperature increases, the system passes through a number of intermediate states of quantum origin and/or corresponding to different distributions of non-stoichiometric defects (cation vacancies) over the crystal lattice. The observed effect is attributed to a high concentration of non-stoichiometric defects, which leads to the defect interaction stimulating their ordering, to loosening of the crystal lattice and to an increase in the diffusion rate. It is suggested that the observed temperature instabilities of properties are typical for other phases with high concentrations of non-stoichiometric defects.     

低膨胀固体材料线膨胀系数的干涉测量方法

固体材料的线膨胀系数在精密仪器产业及高精度实验领域是一个非常重要的物理量,要实现对线膨胀系数较低的固体材料进行测量,通常采用激光干涉的方法。采用光路补偿的方法,即激光干涉仪中两干涉臂同支架来测量低膨胀固体材料的线膨胀系数,不但能够抵消支架膨胀对材料受热伸长的影响,还有效地抵消了地面振动对干涉仪的影响,并能够对线膨胀系数在10-6/℃量级的材料的线膨胀系数进行测量。如果改进试验工艺,且采用条纹稳定技术,该方法可以用于更高量级的线膨胀系数的测量。     

Effect of bump characteristics and temperature variation on the online contact resistance of anisotropic conductive joints

Anisotropic conductive film (ACF) suffers a major drawback in regard to reliability even though it has merits, such as reduction in interconnection distance, high performance, and environmental friendliness. The factor of thermal warpage may lead to a highly unreliable electrical connection in the assembly. The work presented in this paper focuses on the online contact-resistance behavior of the ACF joint during thermal shock and compares the results of two different types of dies (Au/Ni bump and bumpless). For this work, we used a flip chip of 11 × 3 mm² in dimension. The flex substrate used was made of polyimide film with an Au/Ni/Cu electrode and daisy-chained circuit for a matching die-bump pattern. The ACF that was used is an epoxy resin in which nickel and gold-coated polymer balls are dispersed. Tests for three different thermal-cycling profiles (125°C to −55°C, 140°C to −40°C, and 150°C to −65°C) were carried out. The samples bonded at a temperature of 180°C, and a pressure of 80 N was used. The initial contact resistances of Au/Ni bump and bumpless samples were 0.25 ω and 0.4 ω respectively. A comparative study was carried out from the results obtained. The results showed that for the flip-chip-on-flex (FCOF) packages having an Au/Ni bump, the increase in online contact resistance is higher than that of the FCOF packages having bumpless chips. For example, in the thermal-cycling profile of 140°C to −40°C, the online contact resistance for the Au/Ni bump raised to 4.6 ω after 180 cycles, whereas it was only 1.3 ω for the bumpless sample. The bump height and bump materials were found to be the main factor for such variation. Results show that, above the glass-transition temperature (T_g), the ACF matrix becomes less viscous, which reduces its adhesive strength and lets the higher bump height of the chip result in a higher standoff of the package and thus sliding is easier to take place. The responses by the assemblies in hot and cold conditions are examined, and in-chamber behavior of the assembly is studied and explained.     

A continuous contact resistance monitoring during the temperature ramp of anisotropic conductive adhesive film joint

In this study, a systematic experimental work was performed to evaluate the reliability of the anisotropic conductive adhesive film (ACF) joint at high temperature for flip-chip-on-flex (FCOF) assemblies. A four-point probe method was developed to measure the contact resistance at high temperature. Measurement was also conducted along the length of the chip. The correlation between the increased resistance and the failure mechanism was investigated using scanning electron microscopy (SEM). Initially, the contact resistance increased linearly with rising temperature, but later, it increased abruptly. This changeover was related to the glass-transition temperature (T_g) of the ACF matrix. The coefficient of thermal expansion (CTE) is very high at temperatures above T_g; thus, the ACF swells too much, reducing the mechanical contact of the particles with the bump and/or pad. Again, as the adhesive strength becomes weaker at temperatures above the glass transition, it is unable to resist the thermal stress of the flex. The cumulative thermal stress at the edges dislodges the particles from the interconnection. Even below T_g, the thermal stress at the edges is higher than the middle point. Thus, the contact resistance varied from the middle joint of the chip to that of the corner at the same high temperature. To reduce the contact resistance at the corner joint of the FCOF packages bonded by ACF, a square-shaped chip instead of a chip with a higher aspect ratio should be used. It was also suggested to use an adhesive with a higher glass-transition temperature and lower CTE.     

一种低温漂的CMOS带隙基准电压源的研究

为了满足深亚微米级集成电路对低温漂、低功耗电源电压的需求,提出了一种在0.25μm N阱CMOS工艺下,采用一阶温度补偿技术设计的CMOS带隙基准电压源电路。电路核心部分由双极晶体管构成,实现了VBE和VT的线性叠加,获得近似零温度系数的输出电压。T-SPICE软件仿真表明,在3.3 V电源电压下,当温度在-20~70℃之间变化时,该电路输出电压的温度系数为10×10-6/℃,输出电压的标准偏差为1 mV,室温时电路的功耗为5.283 1 mW,属于低温漂、低功耗的基准电压源。     

Study of bending reliability and electrical properties of platinum lines on flexible polyimide substrates

We have experimentally studied the variation in electrical resistance of flexible platinum lines patterned on polyimide foil when they are subjected to circular bending constraints. The lines were patterned by means of standard photolithography and sputtering deposition. Two different photolithography masks were used for comparative evaluation: an un-expensive transparency mask and a standard chromium mask. Measurements of the temperature coefficient of resistance (TCR) and time stability of the resistance have been acquired for lines bent down to 1.25 mm radius of curvature on a customized bending setup, showing good reliability results. The robustness of the lines has been also assessed by registering their change in resistance while bending at different radii of curvature. The lines showed reliability issues for radii of curvature below 1.25 mm, presenting a resistance variation of 19% for transparency mask-fabricated lines and 9% for chromium mask-fabricated lines. The worse reliability performances of transparency mask lines, compared to the chromium mask ones, was found to be due to their imperfect edges, which promoted the formation and propagation of cracks during bending. The results of the experiments in this work permitted to compare the performances of flexible conductive lines with different geometry and fabricated with two different masks, establishing quantitative and qualitative bending limits for their appropriate operation in flexible electronics systems.     

On the profile of temperature dependent series resistance in Al/Si3N4/p-Si (MIS) Schottky diodes

The temperature dependence of capacitance-voltage (C-V) and conductance-voltage (G/w-V) characteristics of metal-insulator-semiconductor (Al/Si₃N₄/p-Si) Schottky barrier diodes (SBDs) was investigated by considering series resistance effect in the temperature range of 80-300 K. It is found that in the presence of series resistance, the forward bias C-V plots exhibit a peak, and experimentally show that the peak positions with a maximum at 260 K shift toward lower voltages with increasing temperature. The C-V and (G/w-V) characteristics confirm that the interface state density (N_ss) and series resistance (R_s) of the diode are important parameters that strongly influence the electric parameters of MIS structures. The crossing of the G/w-V curves appears as an abnormality compared to the conventional behavior of ideal Schottky diode. It is thought that the presence of series resistance keeps this intersection hidden and unobservable in homogeneous Schottky diodes, but it appears in the case of inhomogeneous Schottky diode. In addition, the high frequency (C_m) and conductance (G_m/w) values measured under both reverse and forward bias were corrected for the effect of series resistance to obtain the real diode capacitance.     

基于温度补偿的无运放低压带隙基准源设计

设计了一种带温度补偿的无运放低压带隙基准电路。提出了同时产生带隙基准电压源和基准电流源的技术,通过改进带隙基准电路中的带隙负载结构以及基准核心电路,基准电压和基准电流可以分别进行温度补偿。在0.5μmCMOS N阱工艺条件下,采用spectre进行模拟验证。仿真结果表明,在3.3V条件下,在-20～100℃范围内,带隙基准电压源和基准电流源的温度系数分别为35.6ppm/℃和37.8ppm/℃,直流时的电源抑制比为-68dB,基准源电路的供电电压范围为2.2～4.5V。     

溅射气氛对VOx薄膜结构及性能的影响

溅射总气压一定,通过改变氧氩气体的比例,用射频磁控反应溅射法在玻璃衬底上制备VOx薄膜.用X射线衍射(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、QJ31单臂电桥等测试了不同氧氩比例对VOx薄膜的晶体结构、表面形貌、成分和电阻的影响.测试分析结果表明,氧氩比是影响VOx薄膜结构及性能的重要因素.在我们的实验条件下,最佳氧氩比为2∶25,电阻温度系数为-2.87%/℃.