Foundry Service Research Articles

Thermally actuated microbeam for large in-plane mechanical deflections

The design, finite-element analysis, and experimental performance evaluation of a microelectromechanical systems (MEMS) device, known as a thermally actuated beam, is presented. The behavior of the thermal beam has been characterized so that it can be considered as an actuator in future MEMS applications. A MEMS polysilicon thermally actuated beam uses resistive (Joule) heating to generate thermal expansion and movement. To be a useful MEMS device, a thermally actuated beam will need to produce in-plane tip deflections that span 0–10 μm; while generating force magnitudes on the order of 10 μN. The thermally actuated beam design was accomplished with the L-Edit® software program. The devices were fabricated using the Multi-User Microelectromechanical Systems Process foundry service at the Microelectronics Center of North Carolina. The finite-element modeling analysis was accomplished with the IntelliCAD® computer program. These analyses predicted thermal beam tip deflections (0–13 μm) consistent with experimental observations. The average tip force generated by the thermal beam was measured to be 8.5 μN. The resonant frequency associated with in-plane motion, without damping, was calculated to be 75.16 kHz. The average resonant frequency measured in ambient air was 69.73 kHz. As a relative measure of reliability, it was observed that the thermal beam could be activated well in excess of three million cycles.

Elimination of extra spring effect at the step-up anchor of surface-micromachined structure

This paper describes the concept, analysis, fabrication, and testing of a new anchor for surface-micromachined beams. The anchor is designed to eliminate the extra spring effect at the step-up anchor common in conventional surface-micromachined beams, so that the boundary condition follows the ideal anchoring condition more accurately. The idea is to form a reinforcement hump at the beam anchor through a minor modification in the sacrificial-layer mask. No modification in the fabrication process is necessary. Formation of the reinforcement hump is tested using the multiuser MEMS Process (MUMP) foundry service at the Microelectronics Center of North Carolina (MCNC). The effectiveness of the new anchor is analyzed by finite-element analysis based on the actual anchor geometry obtained from the fabrication directly. Experimental verification is provided by making overhanging microcantilever pairs, one with the new anchor and the other with conventional, through MUMP's and postprocessing and comparing their frequency responses. Small-signal frequency response measurements are made with a modified Michaelson interferometer. Resonant frequency of a 2-/spl mu/m-thick 300-/spl mu/m-long polysilicon cantilever with the new anchor differed by less than 0.1% from the ideal anchor case. In comparison, the resonant frequency of the same beam with a conventional anchor is off by over 1%.

A vertical-cavity surface-emitting laser appliqued to a 0.8-μm NMOS driver

An optoelectronic integrated circuit (OEIC) composed of a vertical-cavity surface-emitting laser (VCSEL) appliqued to an NMOS drive circuit was fabricated to form an optical link from the CMOS chip. A custom NMOS circuit was designed and fabricated through the MOSIS foundry service in a standard 0.8-μm CMOS process. InGaAs quantum-well VCSELs were grown, fabricated and tested on an n-type GaAs substrate. Next, the VCSELs underwent a substrate removal technique and were appliqued to the NMOS circuitry. The OEIC was tested at the chip level and showed an electrical to optical conversion efficiency of 1.09 mW/V. Modulation results are also discussed.

High-voltage devices and circuits fabricated using foundry CMOS for use with electrostatic MEM actuators

Devices and circuits capable of high-voltage operation are necessary for the actuation of micromachined electrostatic structures that require high voltages (20–100 V). These high-voltage devices have traditionally been fabricated using specialized processes. Monolithic integration of the actuators with circuits, including the high-voltage drive, makes it important to provide high-voltage circuit elements in CMOS, which is often the process of choice for signal-processing circuits. Fabrication processes available through foundry services using standard CMOS are attractive to users with no or limited access to clean-room facilities. High-voltage n- and p-type MOS transistors have been fabricated using the 2.0 μm analog CMOS process available through the MOSIS foundry service. By using the n-well and the p-base layers as lightly doped drains, breakdown voltages are 120 V and −27 V for the NMOS and PMOS structures, respectively. The corresponding Early voltages are − 1000 V for the NMOS and 240 V for the PMOS devices. A simple differential amplifier using the high-voltage devices has been fabricated and used to drive all-aluminum electrostatic actuator structures. A first-level SPICE model has also been derived for the high-voltage transistors.

Screen printing: a technology for the batch fabrication of integrated chemical-sensor arrays

The commercialization of integrated chemical sensor has been slowed by the difficulty of device encapsulation and membrane application. For reasons of both cost and reproducibility, the sensor-specific structures should be mass fabricated, as are the microelectronics. The challenge lies in merging the standard semiconductor process sequence with the non-standard steps used to form the transducers. We demonstrate that screen printing can be used to partition the fabrication into two distinct sequences, semiconductor processing and sensor-specific steps. This simplifies process development and evolution, and makes semiconductor foundry services available for manufacturing sensors. After conventional semiconductor processing, our wafers have silver epoxy contacts screen printed on the aluminum sensor pads; the silver forms a stable chemical interface to the membranes, and the epoxy makes a strong physical bond to them. Next, the polymeric membranes are applied and patterned with screen printing. Membranes of different compositions can be deposited on the various sites of a multisensor chip by simply repeating the screen print/cure cycle. We show that the electrochemical performance of mass-fabricated passive and active sensor arrays is comparable to that of conventional liquid-junction ion-selective electrodes.

2.5 Gb/s laser-driver GaAS IC

A laser-diode driver GaAs IC incorporating an optional NRZ/RZ (non-return-to-zero/return-to-zero) conversion facility, having ECL (emitter-coupled logic) and SCFL (source-coupled FET logic)-compatible inputs and providing a 0-60-mA adjustable output current into a 50- Omega /5-V termination at bit rates up to 2 Gb/s NRZ and maintaining a clear eye opening of 50 mA at 2.5 Gb/s NRZ bit rate has been designed, using a commercial 1- mu m gate-length (F/sub tau /=12 GHz) GaAs MESFET foundry service. The high maximum output current is obtained by implementing the output driver as a cascode differential amplifier. The logic circuitry implemented using a novel, DCAL (diode-clamped active-load) SCFL family, which is based on gate-width scaling rather than on absolute values, so that the on-chip logic voltage swing is less sensitive to process variations than conventional SCFL. A 60% improvement in noise margin is also obtained. To verify laser driving performance a back-to-back optical-fiber transmission experiment was performed, giving good optical eye diagrams at 2.5 Gb/s. The electrooptical interplay between laser-diode driver and laser-diode has been demonstrated using SPICE simulations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Fabrication, Performance, and Reliability of InP-Based HBTs

ABSTRACTOver the past 10 years, heterojunction bipolar transistors (HBTs) have progressed to where integrated circuit (IC) products are being sold and foundry services are being commercially offered utilizing gallium arsenide (GaAs) based technology. We will discuss, here, an alternative HBT technology based on indium phosphide (InP). While this technology is less mature than its GaAs counterpart, it offers several attractive benefits in comparison with GaAs. These benefits are provided through several key material properties of InP and ternary compound semiconductors, eg. gallium indium arsenide (GaInAs), grown on the InP. We review the status of this npn HBT technology and present performance results which illustrate the benefits of the technology with respect to electronic applications. Finally, we present measured reliability data for this technology which shows outstanding projected lifetimes.

A normally-off process for analogue/digital GaAs ASICs

An enhancement mode process developed by Philips Research Labs is available through foundry service at Philips Microwave Limeil. This process is meant to address not only purely digital circuits, but also low-cost, ultra low power analogue and analogue-digital mixed functions with high integration density. In this article, an integrated GPS front-end, designed and fabricated by PNL/LEP, is described. This 3-chip receiver includes an integrated VCO, amplifiers, a mixer, a phase frequency comparator, a 2-bit ADC, registers and several prescalers. The outstanding performance measured on this system is believed to lead to a drastic price reduction of the RF receiver, compared with an hybrid implementation.

Electron-beam programming and testing of complementary metal-oxide semiconductor systems

This paper describes the application of a scanning electron beam lithography system (SEBL) to the programming and testing of digital CMOS systems via the direct injection of charge into the integrated circuits. E‐beam programmable interconnect structures, using floating‐gate FETs, implement customization and fault avoidance techniques. E‐beam controlled stimulus/response testing circuits, using substrate diodes, provide access to internal circuit nodes and thereby permit efficient testing procedures for large systems. Two system‐level applications are presented—a digital multiplier and a crosspoint switch. In both cases, redundant circuit components and programmable interconnect are used to achieve fault tolerance and yield enhancement. An analysis of a wafer‐scale crosspoint switch design indicates that e‐beam restructuring techniques could be used to implement an 80×75 element array on a 4‐in. wafer with 99% yield. The e‐beam programming and testing circuits are shown to be compatible with commercial CMOS foundry services. The precision, speed, and automation of the SEBL system make these techniques practical for large‐scale digital systems.

High-speed gallium arsenide for digital integrated circuits

Gallium-arsenide digital ICs able to perform standard functions at operating speeds in excess of 2 Gbit/s are now available from several manufacturers. More spacialist parts are being produced in the research laboratories of systems companies, and by the users of the increasing number of the increasing number of foundry services