Few conferences carry the clout of the IEEE's International Electron Devices Meeting (IEDM). For 51 years, it has been a launching pad for a wide range of semiconductor technologies, including gallium-arsenide (GaAs) transistors, silicon-germanium (SiGe) devices, and lately CMOS micro electromechanical systems (MEMS) components and assemblies. The 2006 edition of this respected semiconductor meeting is scheduled for December 11-13, 2006 at the Hilton San Francisco (San Francisco, CA).

The IEEE IEDM can be considered an official log of semiconductor benchmarks. It is common ground for a wide range of different types of semiconductors, from nanostructure MEMS developments to massive high-power microwave transistors for radar applications. While those interested in advances in process technologies, sensors, memory devices, and computer processors will find them at the 2006 IEEE IEDM, the focus of this report is on RF/microwave-related developments in semiconductor technologies.

Several "breakthrough" type developments will be announced at this year's conference, including wireFET technology-for three-dimensional (3D) integrated circuits. The technique, as reported by Vidra Varadarajan and fellow researches from the Department of Electrical Engineering and Computer Sciences at the University of California at Berkeley (Berkeley, CA) and the Advanced Device Development Division of NEC Corp. (Tokyo, Japan) amounts to fabricating a transistor directly within a wire or interconnect. The process flow consists of forming an aluminum (Al) wire, forming a silicon (Si) island on top of it, and annealing the metal transistor structure below the Al-Si eutectic temperature (+570°C) to cause a layer exchange between the Si and Al. This results in a polycrystalline-Si (poly-Si) region embedded within the wire, which can serve as the channel of a transistor. By applying a bias to the Si substrate, which is electrically isolated from the Al wire by a silicon-dioxide (SiO₂) passivation layer, the resistance of the wire can be modulated. Because the researchers' process is fairly simple and has a low thermal budget, it is thought that their novel wireFET technology could be applied to the implementation of configurable interconnections as well as tunable passive devices in cost-effective 3D ICs.

One relatively new device structure that has the potential to replace bulk MOSFETs because of its superior control of short-channel effects is the Fin-FET. But in order to better understand the novel device, models must be developed in support of computer-aided-engineering (CAE) circuit-simulation tools. G.D.J. Smit and associates from Philips Research Laboratories ( Eindhoven, The Netherlands), IMEC ( Leuven, Belgium), and Arizona State University (Tempe, AZ) offered the results of their work on creating a compact FinFET model for a symmetric three-terminal device with thinly doped or lightly doped body. The accuracy of the model was validated by comparison with measurements on FinFETs wth 30-nm-thick undoped silicon body which was isolated from the substrate by a buried oxide, a metal gate, and SiON gate dielectric. The height of the device's fins was 60 nm, the physical gate length was 110 nm, and a total of 300 fins were fabricated in parallel. Both DC and scattering (S) parameter measurements were performed through 50 GHz. After fitting the model to the DC data, it was apparent that it accurately predicted not only drain current but transconductance as well.

In the area of modeling, T. Esaki and fellow researchers at the Graduate School of Advanced Sciences of Matter at Hiroshima University ( Hiroshima, Japan) presented details on a physics-based photodiode (PD) model with transient current generation explicitly contained in the end results. The model is compatible with conventional compact electrical device models and is ideal for simulation of optoelectric ICs (OEICs). The model includes the optically excited photocurrent and the PD device part solved in the time domain. Predictions from the model were compared with measurements for a single OEIC with a PD and a single MOSFET. The prediction results of the Gaussian distributed electric field exactly capture the laser excitation features shown by the measurements.

One of the more novel developments to be presented at IEDM is a large-area flexible wireless power transmission sheet using printed plastic MEMS switches and organic field-effect transistors (FETs). The research, conducted by Tsuyoshi Sekitani and associates from the Quantum-Phase Electronics Center of the School of Engineering at the University of Tokyo (Tokyo, Japan) and The Center for Collaborative Research at the University of Tokyo, shows the results of a power transmission sheet manufactured using printing process technologies. The position of electronic devices on the sheet (Fig. 1) can be contactlessly sensed by electromagnetic (EM) coupling using the organic transistors. Power is selectively fed to the objects by an EL field using the plastic MEMS switching matrix.

Inspired by unwanted dependence on batteries in wireless systems, the researchers sought a wireless power source. Their solution represents the first step towards building infrastructure for the many electronic devices that are scattered over desks, floors, walls, and ceilings and require power. By using wireless transmission of power to these devices, their batteries can be recharged, or they can even operate directly from the wireless power source.

The wireless power transmission sheet is manufactured on a plastic film. The sheet contains a two-dimensional array of 8 x 8 cells comprising position-sensing and power transmission units. The effective power transmission area is 21 x 21 cm. Once the position of an electronic object on the sheet has been contactlessly sensed by EM coupling using an organic transistor matrix, power is selectively fed to the object by an EM field using a two-dimensional array of copper coils that are driven by a printed plastic MEMS switching matrix. In their experiments with the sheet, 29.3 W of power was wirelessly received with power transmission efficiency of 62.3 percent. The sheet was only 1 mm thick and weighed only 50 g.

The MEMS switching matrix was formed with a combination of ink-jet printing and screen printing. The electrodes for power transmission and for electrostatic attraction are patterned on a 25-micron-thick polyimide membrane. Wireless power transmission was performed at 13.56 MHz with on/off ratio for the MEMS switches of better than 700. The change in the resistance of the MEMS switches after 300,000 switching cycles was less than 5 percent. Among the examples the researchers cited, they used their flexible wireless power transmission sheet to drive 21 light-emitting-diode (LED) lights requiring a total power of 2 W on a Christmas tree.

The use of plastic for electronic devices was also presented by student researchers Brian Mattis and Vivek Subramanian of the Department of Electrical Engineering and Computer Sciences at the University of California at Berkeley in their work on stacked low-power field-programmable antifuse memories for radio-frequency-identification (RFID) devices on plastic. The researchers demonstrated two stacked layers with 100 b/level (a total of 200 b) with programmable energy requirements of a mere 1 nW/b for encoding in low-cost RFID tags. The two layers of the antifuse array used shared electrodes with steering diodes facing in opposite directions. Due to the roughless of the plastic, a smoothing layer of PVP is applied. A 150-nm aluminum electrode is deposited through a shadow mask to form the bottom electrode lines. The antifuse layer is PVP spin-annealed at a relatively low processing temperature of +100°C. The devices allowed programming with 16-V pulses of 25 ns in duration for extremely fast write processes even at that low programmable power of 1 nW/b.

For extremely high-frequency results, few could match the work conducted by William Snodgress and team from the Department of Electrical and Computer Engineering at the University of Illinois at Urbana-Champaign (Urbana, IL). They reported record numbers for pseudomorphic InP/InGaAs heterojunction bipolar transistors with cutoff frequencies to 765 GHz at room temperature (+25°C) and increasing to 845 GHz (Fig. 2) at –55°C with a supply voltage of 1.65 V. The current density at room temperature was 18.7 mA/µm2 with the same results obtained at the lower ambient temperature. The researchers attributed the improved performance at lower temperatures to reduced transistor base and collector transit delays as well as smaller collector charging delays.