Microsensors vs. ICs: a study in contrasts

Significant differences between microsensors and micromechanisms, on the one hand, and integrated circuits, on the other, are examined from the design viewpoint. Microelectronic sensors, micromachining processes, and micromechanisms and micro-actuators are discussed. The principal technological forces driving microsensor development, namely lithography and planar technology, are considered, and some cautionary advice is given regarding the development of so-called smart sensors. Two issues in regard to the partitioning of measurement systems-device partitioning and calibration-are addressed. Technology constraints and packaging considerations are examined     

Development of pNH4-isfets microsensors for water analysis

Front-side connected, N-channel, normally-off, SiO₂/Si₃N₄ chemical field effect transistor (ChemFET) microsensors have been fabricated using a standard P-well silicon technology. These ChemFETs microsensors were adapted to ammonium ion detection thanks to photosensitive polysiloxane (PSX) polymer containing nonactine as an ionophore. The ammonium-sensitive membrane has been deposited either manually by micropipette, either by spin coating and patterned using photolithography technique. Both processes have been studied and compared through the ammonium ion determination. The manually deposed layers have been characterised by thickness non-reproducibility. Therefore, spin-coated layers have good reproducibility, but their thickness of 30 μm has been responsible for an increase of the ISFET threshold voltage and a decrease of its bias current. Nevertheless, in both cases, good sensitivities have been shown on the (1-5) pNH₄ range even if saturation phenomena have been evidenced for the lowest concentrations. These pNH₄-ISFETs microsensors are developed for the monitoring of environmental pollution and more precisely for ground water analysis.     

Implementation of multichannel sensors for remote biomedical measurements in a microsystems format

A novel microelectronic "pill" has been developed for in situ studies of the gastro-intestinal tract, combining microsensors and integrated circuits with system-level integration technology. The measurement parameters include real-time remote recording of temperature, pH, conductivity, and dissolved oxygen. The unit comprises an outer biocompatible capsule encasing four microsensors, a control chip, a discrete component radio transmitter, and two silver oxide cells (the latter providing an operating time of 40 h at the rated power consumption of 12.1 mW). The sensors were fabricated on two separate silicon chips located at the front end of the capsule. The robust nature of the pill makes it adaptable for use in a variety of environments related to biomedical and industrial applications.     

Ohmic-Contact Technology for GaN-Based Light-Emitting Diodes: Role of P-Type Contact

GaN-based semiconductors are of great technological importance for the fabrication of optoelectronic devices, such as light-emitting diodes (LEDs) and laser diodes. The further improvement of LED performance can be achieved through the enhancement of external quantum efficiency. In this regard, high-quality p-type ohmic electrodes having low contact resistance and high transmittance (or reflectivity), along with thermal stability, must be developed because p-type ohmic contacts play a key role in the performance of LEDs. In this paper, we review recent advances in p-type ohmic-contact technology for GaN-based LEDs. A variety of methods for forming transparent and reflective ohmic contacts are introduced.     

具有电流阻挡层的垂直结构氮化镓发光二级管的光电特性研究

本文对具有电流阻挡层（CBL）的氮化镓垂直结构发光二极管（LED）进行了研究。不带有CBL、带有非欧姆接触CBL和带有二氧化硅CBL的垂直LED芯片样品被制作出来,并对它们进行了光电性能的测试。结果表明这种带有非欧姆接触CBL和带有二氧化硅CBL的氮化镓垂直结构LED的光输出效率相比不带有CBL的分别高出40.6%和60.7%。不带有CBL的、带有非欧姆接触CBL和带有二氧化硅CBL的氮化镓垂直结构LED在350毫安下的效率分别下降到各自最高效率的72%、78%和85.5%。另外,带有非欧姆接触CBL的氮化镓垂直结构LED具有更优越的抗静电性能。     

Optical and electrical characteristics of GaN vertical light emitting diode with current block layer

A GaN vertical light emitting diode(LED)with a current block layer(CBL)was investigated.Vertical LEDs without a CBL,with a non-ohmic contact CBL and with a silicon dioxide CBL were fabricated.Optical and electrical tests were carried out.The results show that the light output power of vertical LEDs with a non-ohmic contact CBL and with a silicon dioxide CBL are 40.6%and 60.7%higher than that of vertical LEDs without a CBL at 350 mA,respectively.The efficiencies of vertical LEDs without a CBL,with a non-ohmic contact CBL and with a silicon dioxide CBL drop to 72%,78%and 85.5%of their maximum efficiency at 350 mA,respectively. Moreover,vertical LEDs with a non-ohmic contact CBL have relatively superior anti-electrostatic ability.     

Study of front-side connected chemical field effect transistor for water analysis

Front-side connected, N-channel, normally-off, chemical field effect transistor (ChemFET) microsensors including a SiO₂/Si₃N₄ pH-sensitive gate have been fabricated using a standard P-well silicon technology. The fabrication and packaging processes are described and sensor properties and performances are demonstrated through pH measurements. Finally, the front-side connected ChemFETs microsensors have been adapted to the detection of ions thanks to polyHEMA/siloprene-based ionosensitive membranes. Application is performed through the NH₄⁺ and NO₃⁻ ions detection in artificial solutions, evidencing quasi-Nernstian responses (s≈50 mV/pH) in the appropriate detection ranges. This microsensor will be used for the monitoring of environmental pollution and more precisely for ground water analysis.     

Transfer of GaN-Based Light-Emitting Diodes From Silicon Growth Substrate to Copper

III-nitride light-emitting diodes (LEDs) grown on Si (111) substrates have the potential of low-cost manufacturing for solid-state lighting and display, by taking advantage of the well-developed IC technologies of silicon. In this letter, LEDs grown on silicon substrates were transferred onto copper substrates, to maximize light extraction and heat dissipation. On Si substrates, $hbox{300} times hbox{300} muhbox{m}^{2}$ multiple quantum well InGaN LEDs were first grown and processed. The top surface of the fabricated devices was then temporarily bonded to a sapphire wafer and the Si substrate was chemically etched. Ti/Al/Ti/Au layers were deposited on the backside of LEDs. An 80-$muhbox{m}$ -thick copper layer was electroplated and the temporary bonding was removed, resulting in LEDs on copper substrate. The optical output power of LEDs on copper increased by $sim$ 70% as compared to that of the LEDs on silicon. The improved performance was attributed to the removal of the light-absorbing Si substrate and the good thermal conductivity of copper.      

Silicon micromechanics: sensors and actuators on a chip

The techniques used to fabricate micromechanical structures are described. Bulk micromachining is routinely used to fabricate microstructures with critical dimensions that are precisely determined by the crystal structure of the silicon wafer, by etch-stop layer thicknesses, or by the lithographic masking pattern. Silicon fusion bonding has been used to fabricate micro silicon pressure sensor chips. Surface micromachining, based on depositing and etching structural and sacrificial films, allows the designer to exploit the uniformity with which chemical vapor deposition (CVD) films coat irregular surfaces as well as the patterning fidelity of modern plasma etching processes. Silicon accelerometers, resonant microsensors, motors, and pumps made by these techniques are discussed. Measuring the mechanical properties of silicon, which are important to these applications, is examined     

Technological processes and modeling of opto-electro-mechanical microstructures

Micromachining is a promising technology for the development of microsensor applications, based on integrated optics circuits. This paper presents technological processes for fabrication of an opto-electro-mechanical microstructure. Optical waveguides were integrated with photodiodes and three-dimensional structures (cantilevers) on a silicon substrate. We performed different analyses for reducing the induced tensile stress in the mechanical parts. We estimated the stress using ANSYS modeling.     

Direct bonding of GaAs films on silicon circuits by epitaxial liftoff

Epitaxial liftoff has emerged as a viable technique to integrate GaAs with silicon. The technique relies on the separation of a thin epi-GaAs film from its substrate followed by direct bonding of the thin film to a silicon substrate. The silicon substrate has to meet certain planarity and smoothness conditions in order to obtain high quality bonding. Unfortunately, processed silicon IC chips do not satisfy these conditions. In this paper, we report on the results of two different planarization techniques, plasma etch back and chemical-mechanical polishing, to integrate GaAs LEDs with silicon circuits using epitaxial liftoff. 4 by 8 arrays of GaAs LEDs have been integrated with silicon driver circuits using plasma etch back. We also have lifted off areas as large as 500 mm² and bonded them on 5″ device wafers by chemical-mechanical polishing. This can be essential for mass production of optoelectronic devices based on epitaxial liftoff.     

Horizontal current bipolar transistor (HCBT): a new concept ofsilicon bipolar transistor technology

A new concept of silicon bipolar transistor technology is proposed. The resulting horizontal current bipolar transistor (HCBT) is simulated assuming the 0.25 μm technology. The surface of the device is smaller than conventional super-self aligned bipolar transistors. The same doping profile as in known vertical current devices is achieved by simpler technology using single polysilicon layer, without conventional epitaxial and n⁺ buried layers and with reduced number of lithography masks and technological steps. The simulated dc and ac characteristics of HCBT are similar to the characteristics of standard SST devices     

Spectroscopic detection of gastrointestinal dysplasia using optical microsensors

The detection of dysplasia in the gastrointestinal tract can be performed using optical microsensors based on thin-film optical filters and silicon photodiodes. This paper describes two optical microsensors that can be used for spectroscopy data collection in two different spectral bands (one in the violet/blue region and the other in the green region) for which two optical filters were designed and fabricated. An empirical analysis of gastrointestinal spectroscopic data using these specific spectral bands is performed. The obtained results show that it is possible to accurately differentiate dysplastic lesions from normal tissue, with a sensitivity and specificity of 77.8% and 97.6%, respectively. Therefore, the developed filters can be used as a tool to aid in diagnosis. The small size of the optical microsensors can enable, in the future, integration in endoscopic capsules.     

Blue flip-chip AlGaInN LEDs with removed sapphire substrate

Characteristics of AlGaInN LEDs with removed sapphire substrate are studied. To remove the substrate from a finished LED crystal mounted by the flip-chip method onto a silicon wafer, the laser lift-off technique was used. To raise the light output efficiency, a scattering profile was formed on the n-GaN surface by ion etching in a Cl₂: Ar gas mixture. This resulted in the 25–30% increase in the external quantum efficiency of LEDs. The LEDs fabricated in this way demonstrate stable operation at drive currents of up to 300 mA with an optical power as high as 110 mW.     

Microactuators and their technologies

This paper gives a brief overview of microactuators, focussing on devices made by microfabrication technologies which are based on silicon processes like photolithography, etching, thin film deposition etc. These technologies enable the miniaturization of electrical devices as well as micromechanisms and microactuators. They can be batch fabricated on large area silicon substrates and represent the smallest available in a vast field of actuators. Mentioning the activation principles and the three main fabrication technologies: bulk micromachining, surface macromachining and moulding, the paper focusses on devices, which made their way into industrial applications or prototypes. The far most developed micro electro-mechanical systems (MEMS) are found in micro-fluidic systems (printheads, microvalves and -pumps) and micro-optical systems (micromirrors, -scanners, -shutters and -switches). They can be combined with microelectronics and microsensors to form an integrated on-chip or hybrid-assembled system. Other MEMS-actuators like microgrippers, microrelays, AFM heads or data storage devices, are promising devices for future medical, biological and technical applications like minimal invasive surgery or the vast field of information storage and distribution.     

晶圆键合技术在LED应用中的研究进展

简要介绍了晶圆键合技术在发光二极管(LED)应用中的研究背景,分别论述了常用的黏合剂键合技术、金属键合技术和直接键合技术在高亮度垂直LED制备中的研究现状,包括它们的材料组成和作用、工艺步骤和参数以及优缺点.其中,黏合剂键合是一种低温键合技术,且易于应用、成本低、引入应力小,但可靠性较差;金属键合技术能提供高热导、高电导的稳定键合界面,与后续工艺兼容性好,但键合温度高,引入应力大,易造成晶圆损伤;表面活化直接键合技术能实现室温键合,降低由于不同材料间热失配带来的负面影响,但键合良率有待提高.     

Silicon integrated photonics begins to revolutionize

The advances in Si technology and the rapid growth of broadband communication via optical fiber allow silicon integrated photonics to begin revolutionizing the electronic devices, circuits, and systems. The pace of technological development has been recently speeded up. Using microfabrication technology we are now able to make waveguide structures and optical components from Si-based materials, such as silicon oxynitride or doped silica. Visible light can be obtained from Si-based materials such as Si quantum wire/dots and Si nanoclusters embedded in insulators. The remaining issues are to develop processes and device structures to make Si photonics economically viable with system and device performance comparable to their existing counterparts. Recent efforts have demonstrated that the light-emitting efficiency can be enhanced greatly and that the lasing effect is also possible with the nanostructures. The impact of these moves will be revolutionary. The successful development of Si integrated photonics will enable on-chip optical interconnects for future microprocessor and giga-scale circuits, chip-to-chip fiber interconnection and will greatly decrease the cost for fiber-to-home connection. This will be one of the major moves for the next technology revolution. The present article discusses some recent developments on these aspects.     

Direct bonding in patent literature

Patent literature tells its own story of technological innovations. This story is evaluated here in the case of direct bonding. It is concluded that, on a worldwide basis, direct bonding has been approached via three avenues: optical, silicon technology and silicon wafer preparation.     

Light-emitting diodes based on colloidal silicon quantum dots

Colloidal silicon quantum dots (Si QDs) hold great promise for the development of printed Si electronics. Given their novel electronic and optical properties, colloidal Si QDs have been intensively investigated for optoelectronic applications. Among all kinds of optoelectronic devices based on colloidal Si QDs, QD light-emitting diodes (LEDs) play an important role. It is encouraging that the performance of LEDs based on colloidal Si QDs has been significantly increasing in the past decade. In this review, we discuss the effects of the QD size, QD surface and device structure on the performance of colloidal Si-QD LEDs. The outlook on the further optimization of the device performance is presented at the end.     

Light emitting diodes reliability review

The increasing demand for light emitting diodes (LEDs) has been driven by a number of application categories, including display backlighting, communications, medical services, signage, and general illumination. The construction of LEDs is somewhat similar to microelectronics, but there are functional requirements, materials, and interfaces in LEDs that make their failure modes and mechanisms unique. This paper presents a comprehensive review for industry and academic research on LED failure mechanisms and reliability to help LED developers and end-product manufacturers focus resources in an effective manner. The focus is on the reliability of LEDs at the die and package levels. The reliability information provided by the LED manufacturers is not at a mature enough stage to be useful to most consumers and end-product manufacturers. This paper provides the groundwork for an understanding of the reliability issues of LEDs across the supply chain. We provide an introduction to LEDs and present the key industries that use LEDs and LED applications. The construction details and fabrication steps of LEDs as they relate to failure mechanisms and reliability are discussed next. We then categorize LED failures into thirteen different groups related to semiconductor, interconnect, and package reliability issues. We then identify the relationships between failure causes and their associated mechanisms, issues in thermal standardization, and critical areas of investigation and development in LED technology and reliability.