N.G. Tarr

24 GHz On-Chip Antennas and Balun on Bulk Si for Air Transmission

The conditions are investigated under which standard digital bulk Si technology can yield efficient on-chip antennas and baluns for fully differential transmitter and receiver implementations. The effects of the IC material properties and the antenna geometry on radiation and impedance characteristics have been studied. 24 GHz on-chip antennas on lossy Si have been successfully demonstrated, using a standard IC fabrication compatible Cu process. The fabricated antennas demonstrate a gain ranging from 8- to - 10.5 dBi, which is to the best of the authors knowledge, the highest gain reported for antennas in a 10 Omega-cm Si substrate to date.

A sensitive, temperature-compensated, zero-bias floating gate MOSFET dosimeter

A new MOSFET dosimeter consisting of a floating gate sensor transistor and a reference transistor of identical geometry fabricated in close proximity on the same silicon chip is described. Sensitivity is maximized by not overlapping the floating gate with a control gate. The floating gate is precharged prior to irradiation by tunneling. No bias is applied during irradiation. The dosimeter output is the reference transistor gate bias required to give the same drain current in the sensor and reference MOSFETs at the same drain-source bias. Sensitivities up to 3 mV/rad have been achieved. The dosimeter provides excellent first-order temperature compensation. With second-order temperature compensation using an external temperature sensor, doses less than 500 mrad should be resolvable.

A floating gate MOSFET dosimeter requiring no external bias supply

MOSFET dosimeters incorporating an electrically floating polysilicon gate have been fabricated in a commercial CMOS technology. Charge is placed on the floating gate by tunnelling from a small overlapping injector gate. Subsequent irradiation partially discharges the floating gate, producing a change in threshold voltage which can be used to infer the absorbed dose. No external power source is required during this sensing period. Sensitivities up to 70 mV Gy/sup -1/ (0.7 mV/rad) have been obtained for temperature-compensated matched-pair dosimeters under /sup 60/Co gamma irradiation.

A 27 GHz fully integrated CMOS distributed amplifier using coplanar waveguides

This paper reports a CMOS distributed amplifier which operates from 1-27 GHz. This amplifier exhibits a measured gain of 6 dB and uses coplanar waveguides to implement required inductances. Power consumption is 68.1 mW while driven from a 3.3V supply but it can operate with supply voltages as low as 1.8V. Chip area is 1.8 /spl times/ 0.9 mm. To the authors knowledge this is the fastest frequency of operation ever reported for a distributed amplifier implemented in a standard CMOS technology.

Post-processed Cu inductors with application to a completely integrated 2-GHz VCO

A simple post-processing technique allowing Cu inductors to be added to integrated circuits fabricated in technologies providing only Al metallization is presented. The inductors use a 4-/spl mu/m thick electroless plated Cu layer to minimize resistance, and are formed over a 9-/spl mu/m thick polyimide dielectric to reduce substrate losses. Inductors optimized for 2.5-GHz had Q as high as 17. The effectiveness of the post-processing technique is demonstrated by application to a voltage-controlled oscillator (VCO) fabricated in a commercial bipolar technology with Al metallization. Circuits with post-processed Cu inductors gave a phase noise of -106 dBf/Hz at 100 kHz offset from a 2-GHz carrier, while control circuits with Al inductors gave a phase noise of only -101 dBc/Hz at 100 kHz offset from a 1.8-GHz carrier and had higher power consumption.

A polysilicon emitter solar cell

A new solar cell structure is reported in which the emitter consists of a thin layer of in situ phosphorus-doped polysilicon deposited by a low-pressure chemical vapor deposition (LPCVD) techniques. The highest process temperature required to fabricate this structure is only 627°C. Although the use of a polysilicon emitter results in some degradation in blue response, both theoretical and experimental results are presented indicating that photocurrent densities in excess of 30 mA.cm-2are attainable under AM1 illumination. The low back-injection current associated with the polysilicon emitter has allowed a very high open circuit voltage of 652 mV to be obtained at 28°C in a cell illuminated to give a short circuit current density of 30 mA.cm-2.

Sub-micron optical waveguides for silicon photonics formed via the local oxidation of silicon (LOCOS)

In this paper we report a novel fabrication technique for silicon photonic waveguides with sub-micron dimensions. The technique is based upon the Local Oxidation of Silicon (LOCOS) process widely utilised in the fabrication of microelectronics components. This approach enables waveguides to be fabricated with oxide sidewalls with minimal roughness at the silicon/SiO2 interface. It is also sufficiently flexible to enable the depth of the oxidised sidewall to be varied to control the polarisation performance of the waveguides. We will present preliminary results on submicron waveguide fabrication and loss characteristics (less than 1 dB/cm), as well as effects of varying waveguide width on modal properties of the waveguides. We consider the ease of fabrication, as well as the quality of the devices produced in preliminary experimental fabrication results, and compare the approach to the more conventional requirements of high resolution photolithographically produced waveguides. We also discuss preliminary optical results, as measured by conventional means. Issues such as the origins of loss are discussed in general terms, as are the fabrication characteristics such as waveguide wall roughness and waveguide profile. We will discuss further work that will help to establish the potential of the technique for future applications.

Limitations on MOSFET dosimeter resolution imposed by 1/f noise

A sensitive microcomputer-controlled MOSFET-based dosimeter system has been constructed to examine the effects limiting the ability of MOSFET dosimeters to detect very small radiation doses. It is shown that the dose resolution of this system is limited by 1/f noise in the sensor MOSFETs themselves. Doses below 1 mGy (100 mrad) can be detected. Structural changes to the sensor MOSFETs that might provide further improvements in resolution through reduction of 1/f noise are discussed.

Distribution of base dopant for transit time minimization in a bipolar transistor

A means to determine the doping profile minimizing base transit time in a bipolar transistor is presented, assuming that the width of the neutral base is held constant. It is found that the optimum profile is not close to the exponential decrease from emitter to collector predicted by earlier studies.

Composition grading for base transit time minimization in SiGe-base heterojunction bipolar transistors

Abstract A simple iterative procedure for approximation of the germanium composition profile minimizing base transit time in an SiGe alloy base HBT is developed. Two variants of the procedure are presented: one applicable when the germanium concentration is specified at the edges of the base, and the other when the total germanium content in the base is given. In the latter case the optimum Ge profile has a smaller slope near the emitter and a larger slope near the collector than does a linear ramp. In the former case the optimum profile approximates a linear ramp over the central portion of the base, but becomes retrograde near the collector.