Static induction transistor image sensors

New image sensors, based on the operational principle of static induction transistor (SIT), are described in this paper. Two operational modes of SIT image sensors are described here. One is the electron-accumulation mode in which electrons are stored in the floating-cell region and another is the electron-depletion mode in which electrons are removed from the floating-cell region in response to optical input. The electron-depletion mode is superior to the electron-accumulation mode in the charge retention characteristics, its temperature dependence, and the operational tolerancy. The described SIT image sensors, which utilize the vertically configured SITM structure, are very promising for application in very-large-area image converters due to high-speed high-packing density, and wide dynamic range, and especially due to extremely low power dissipation.     

Contact effects in organic thin-film transistor sensors

Contact effects in organic thin-film transistors (OTFTs) sensors are here investigated specifically respect to the gate field-induced sensitivity enhancement of more than three orders of magnitude seen in a DHα6T OTFT sensor exposed to 1-butanol vapors. This study shows that such a sensitivity enhancement effect is largely ascribable to changes occurring to the transistor channel resistance. Effects, such as the changes in contact resistance, are seen to influence the low gate voltage regime where the sensitivity is much lower.     

Degradation of the parameters of transistor temperature sensors under the effect of ionizing radiation

The influence of the effective concentration of an impurity specifying the conduction type of the base region and the base thickness on the radiation resistance of transistor temperature sensors is investigated. The dependences of the forward voltage drop at the emitter transistor junction and current amplification factor on the magnitude of electron, neutron, and γ-quanta flows are revealed. It is found that degradation of the forward voltage drop under the effect of ionizing radiation begins at doses higher by almost two orders of magnitude than the current amplification factor depending on the transistor’s design features. The reproducibility of the temperature-sensitive parameter, which increases the yield percentage of suitable devices, increases after annealing of the electron-irradiated structures.     

Operating principles of bipolar transistor magnetic sensors

Dual-collector bipolar transistor structures have been evaluated and found to be sensitive to an applied magnetic field. In particular, the magnetic field results in unequal currents to the two collectors. The output signal is taken as a differential voltage developed across the output load resistors. The mechanism giving rise to the unequal collector currents appears to be emitter-injection modulation caused by the applied magnetic field. The magnetic field causes the injection from one portion of the emitter to be enhanced while suppressing injection elsewhere thus setting up unequal currents to the two collectors. A simplified theory is presented to explain the behavior of these devices. The theory is found to be in general agreement with experimental results obtained from a number of different device configurations.     

石墨烯场效应管制备的关键工艺研究

近年来,石墨烯因其独特的物理化学性质备受关注,但石墨烯的零带隙结构,限制了它在光电领域方面的应用。研究了石墨烯场效应管制备的关键工艺,即用石墨烯图形化打开其带隙,并在1 cm×1 cm的石墨烯薄膜上制备出大规模、多尺寸的微结构石墨烯场效应管。通过对石墨烯场效应管关键工艺的优化研究,如石墨烯的无损转移、石墨烯条带的刻蚀、光刻胶的选择、金属蒸镀以及退火等工艺,为石墨烯场效应管的进一步研究提供了可靠的工艺参考。     

基于单根酞菁铜纳米线的FET式H_2S气体传感器

结合FET和一维微纳材料的优势,构筑了具有高灵敏度和低检测极限的FET式H2S气体传感器。研究结果发现,在室温条件下,器件对体积分数5×10–6至50×10–6的H2S具有良好的灵敏度和低检测极限(5×10–6)。相比于薄膜FET传感器,检测极限降至原来的1/20。与PMMA绝缘层比较研究结果显示:引起器件对H2S的高器件性能的原因主要归因于被暴露的导电沟道和微纳材料的性质。     

Single-mode-fibre point and extended temperature sensors

The response of single-mode fibres to time-varying thermal perturbations has been characterised by using a Mach-Zehnder interferometer. It is shown that single-mode fibres offer the possibility of high-speed, high-sensitivity remote temperature sensing with a minimum disturbance of the thermal environment and the capability to operate in an electro-magnetically active environment. In addition, fibre temperature sensors can be configured to measure not only the specific temperature at any given point, but also offer the unique feature of extended temperature measurements over the length of a fibre segment in which the device optically integrates any thermally induced fluctuations.     

Organic thin-film transistor sensors: Interface dependent and gate bias enhanced responses

Organic thin film transistors are a new class of sensors potentially capable of outperforming chemiresistors. They can be operated at room temperature, offer the advantage of remarkable response repeatability and can function as multi-parameter sensors. In this paper, evidence of OTFT response dependence on important parameters such as the chemical nature of the organic semiconductor active layer and the gate-dielectric/organic-semiconductor interface are produced. A sizable response enhancement of an OTFT sensor operated in the enhancement mode is also presented indicating that an OTFT can in principle lead to a lower detection limit than a resistor-type sensor with the same organic semiconductor.     

MMST manufacturing technology-hardware, sensors, and processes

This paper describes the equipment and processes utilized in the Microelectronics Manufacturing Science and Technology (MMST) program. The processes were carried out in a combination of testbeds (AVP, the TI designed and built Advanced Vacuum Processor) and commercial equipment, all in the single-wafer mode. All AVP processing was performed with the wafers in an inverted, face-down, configuration. All the processing equipment was connected to a Computer-Integrated Manufacturing (CIM) system, which both collected the designated data and communicated the process parameters from the CIM database to the particular processing unit. Where available, in situ sensors were utilized for monitoring the process parameters, with measurements made on a metrology die in the center of the wafer. Many of these processes were controlled by the model-based process control algorithms in the CIM system. Otherwise, the processes were controlled by standard statistical process control (SPC) methods. This paper emphasizes the processing methodology that was developed and followed in order to operate in this CIM environment and successfully execute an approximately 150 step 0.35 μm CMOS process in less than 72 hours     

Novel resonant tunneling transistor with high transconductance atroom temperature

A resonant tunneling transistor (RTT) utilizing a novel heterodimensional Schottky gate technology is described. The gate is formed by electroplating Pt/Au onto the side of an AlGaAs/GaAs double barrier structure. The gate voltage modulates the drain current by modulating the area of the quasi-two dimensional electron accumulation layer which forms above the source barrier under drain-source bias. Room temperature transistor characteristics included a peak current of 225 mA/mm and peak transconductance of 218 mS/mm. The ultrafine fabrication process is also discussed     

Low temperature poly-Si thin-film transistor fabrication bymetal-induced lateral crystallization

A new low temperature crystallization method for poly-Si TFTs was developed: Metal-Induced Lateral Crystallization (MILC). The a-Si film in the channel area of a TFT was laterally crystallized from the source/drain area, on which an ultrathin nickel layer was deposited before annealing. The a-channel poly-Si TFTs fabricated at 500°C by MILC showed a mobility of 121 cm²/V·s, a threshold voltage of 1.2 V, and an on/off current ratio of higher than 10⁶ . These electrical properties are much better than TFTs fabricated by conventional crystallization at 600°C     

Quantum-well resonant tunneling bipolar transistor operating at room temperature

The first resonant tunneling bipolar transistor (RBT) is reported. The AlGaAs/GaAs wide-gap emitter device, grown by molecular beam epitaxy (MBE), contains a GaAs quantum well and two AlAs barriers between the emitter and the collector. In the common emitter configuration, when the base current exceeds a threshold value, a large drop in the collector current (corresponding to a quenching of the current gain β) is observed at room temperature, along with a pronounced negative conductance as a function of the collector-emitter voltage. These striking characteristics are caused by the quenching of resonant tunneling through the double barrier as the conduction band edge in the emitter is raised above the bottom of the first quantized subband of the well. Single-frequency oscillations are observed at 300 K. The inherent negative transconductance of these new functional devices is extremely valuable for many logic and signal processing applications.     

Fabrication technique for Si single-electron transistor operatingat room temperature

A Si single electron transistor (SET) was fabricated by converting a one-dimensional Si wire on a SIMOX substrate into a small Si island with a tunnelling barrier at each end by means of pattern-dependent oxidation. With this structure, the total capacitance was reduced to ~2aF, which enabled conductance oscillation of the SET at room temperature     

A study of temperature field in a GaN heterostructure field-effect transistor

This paper presents a three-dimensional finite element based heat transfer model for a Gallium Nitride-based Heterostructure Field-Effect Transistor (henceforth referred to as GaN HFET). Analyses were carried out to study the distribution of temperature in the HFET under steady-state conditions for two different steady-current inputs. Two different substrates for the HFET, sapphire and silicon carbide (SiC), were studied. The paper discusses the effect of using a heat sink and also that of using reasonable contact resistances on the substrate side of the HFET, on the temperature profile. In all cases, the gate region of the HFET was found to attain the highest temperature. Subsequent experiments to validate the results of the computational analysis were carried out at the Oakridge National Laboratories, Knoxville, and are also presented in this paper.     

Organic field-effect transistor based sensors with sensitive gate dielectrics used for low-concentration ammonia detection

A novel organic field-effect transistor (OFET)-sensor concept is presented based on the application of an ion-conducting organic dielectric material, which is chemically adapted to change its electronic properties upon contact with an analyte, thereby generating an electrically detectable response. By employing pH-sensitive, ring-opening metathesis polymerized materials as gate dielectrics in bottom-contact OFETs with a meander-shaped top-gate structure, the concept was successfully realized and evaluated with ammonia (NH₃) as gaseous analyte, easily providing distinct sensor response at concentration levels as low as 100 ppm. In addition to current–voltage OFET-analysis, optical spectroscopy and capacitance measurements were used to rationalize the underlying sensor mechanism, which is mainly attributed to a deprotonation of the pH-sensitive groups of the active-sensing dielectrics by NH₃ and a resulting generation of mobile ions, leading to an increase of the charge carrier density within the OFET channel. The proposed concept provides several advantages over existing OFET-sensor detection principles, including the separation of the sensing mechanism from the charge-transport functionality of the semiconductor, inherent protection of the latter against air exposure and increased selectivity by the application of specific dielectric materials. It therefore offers a great deal of promise in contributing to the development of cheap, integrated, smart and flexible (bio)sensor systems.     

On contact resistance measurement using four-terminal Kelvinstructures in advanced double-polysilicon bipolar transistor processes

The contact between a polycrystalline silicon (polysilicon) layer and a silicon substrate is investigated for an advanced double-polysilicon bipolar transistor process. Contact resistances are measured using four-terminal cross bridge Kelvin structures. The specific contact resistivity of the interface and the sheet resistance of the doped substrate region directly underneath the contact are extracted using a two-dimensional simulation model originally developed for metal-semiconductor contacts. The extracted sheet resistance values are found to be larger than those measured using van der Pauw structures combined with anodic oxidation and oxide removal. During the fabrication of the contacts, epitaxial realignment of the polysilicon in accordance to the substrate orientation and severe interdiffusion of dopants across the interface take place, which complicate the characterization. The validity of the two-dimensional simulation model applied to the poly-mono silicon contact is discussed     

氧化钨基室温气敏传感器的研究进展

氧化钨(WO_3)基半导体气体传感器对NO_2等气体具有较好的气敏特性。为了将传感器工作温度降低至室温,研究者们尝试了各种方法,如合成新型纳米材料、紫外光和可见光照射等。主要介绍了近年来WO_3基气敏材料在室温条件下其气敏性能的最新研究进展,展现了近年来WO_3基室温气体传感器的最新研究成果。并提出通过合成具有p-n异质结构的材料、开发新型纳米结构、增加材料中氧空位浓度以减小材料带隙宽度有可能是WO_3室温气体传感器下一下阶段的研究重点。     

温湿度传感器的原理及应用

介绍了温湿度传感器DHT90的主要特点、工作原理、典型应用实例及应用程序。     

Fast temperature programmed sensing for micro-hotplate gas sensors

We describe an operating mode of a gas sensor that greatly enhances the capability of the device to determine the composition of a sensed gas. The device consists of a micromachined hotplate with integrated heater, heat distribution plate, electrical contact pads, and sensing film. The temperature programmed sensing (TPS) technique uses millisecond timescale temperature changes to modify the rates for adsorption, desorption, and reaction of gases on the sensing surface during sensor operation. A repetitive train of temperature pulses produces a patterned conductance response that depends on the gas composition, as well as the temperature pulse width, amplitude, and specific sequence of pulses. Results are shown for the vapors of water, ethanol, methanol, formaldehyde, and acetone