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Papers by Douglas Buchanan

2020 IEEE International Ultrasonics Symposium (IUS), 2020

This paper presents a theoretical model and an experimental validation of a two-port multiple mov... more This paper presents a theoretical model and an experimental validation of a two-port multiple moving membrane capacitive micromachined ultrasonic transducer. The developed transducer includes a stack of two flexible membranes suspended on a fixed electrode. The transducer is fabricated utilizing a sacrificial technique, PolyMUMPs, and with a resonant frequency of 1.8 MHz. Electrical measurements are conducted using an impedance analyzer in order to investigate the influence of the transducer's additional moving membrane on the device effective cavity height. This, consequently, influences the transducer acoustic power generation. The deigned two port transducer enables a dynamic change in the effective cavity height through adjusting the applied DC bias voltage. The experimental results validate this hypothesis and are shown in agreement with the theoretical results.

Journal of Micro/Nanolithography, MEMS, and MOEMS, 2016

Abstract. A multiple moving membrane capacitive micromachined ultrasonic transducer has been deve... more Abstract. A multiple moving membrane capacitive micromachined ultrasonic transducer has been developed. This transducer cell structure includes a second flexible plate suspended between the transducer top plate and the fixed bottom electrode. The added plate influences the transducer top plate deflection map and, therefore, the transducer properties. Three series of individual air-coupled, dual deflectable plate transducers and two 1×27 element transducer arrays were fabricated using multiuser microelectromechanical systems (MEMS) processes (MUMPs). Each set of transducers included devices with middle plate radii from 22% to 65% of the corresponding transducer top plate radius. The effect of the transducer middle plate configuration has been investigated. Electrical, optical, and acoustic characterizations were conducted and the results were compared with the simulation findings. It was found that the transducer top plate amplitude of vibration is significantly enhanced with a wider middle deflectable plate. The electrical and optical measurement results are shown to be in good agreement with simulation results. The acoustic measurement results indicated a 37% increase in the amplitude of transmitted signal by the 1-MHz air-couple transducer when its middle plate radius was increased by 35%.

The Effect of Silicide Formation on the Electrical Properties of Gate Oxides

MRS Proceedings, 1992

ABSTRACTCoSi2, or TiSi2 formation on gate polysilicon can degrade the current-voltage and capacit... more ABSTRACTCoSi2, or TiSi2 formation on gate polysilicon can degrade the current-voltage and capacitance-voltage characteristics of MOS capacitors. Degradation of the gate oxide breakdown field is much more severe for capacitors with TiSi2 than for those with COSi2 TEM reveals evidence for a reaction at the interface between TiSi2 and SiO2, whereas there is no observable reaction between COSi2 and SiO2- The low breakdown fields for devices with TiSi2 may be due to thinning of the gate oxide by the interfacial reaction or mechanical deformation. A high density of electron traps and a small reduction in the breakdown field is observed when COSi2 contacts the gate, possibly due to a compressive stress in the oxide exerted by the suicide. In addition, an increase in the interface state density at the Si-SiO2 interface is seen for all samples exposed to a rapid thermal anneal (RTA) at 800°C, possibly due to the release of H from dangling bonds.

Internaltional Ultrasonics Symposium, Oct 23, 2014

Multiple moving membrane, capacitive micromachined ultrasonic transducers (M3-CMUTs) benefit from... more Multiple moving membrane, capacitive micromachined ultrasonic transducers (M3-CMUTs) benefit from a multiple vibrating membrane configuration that enhances the transducer properties. In this work, further improvement in the device displacement amplitude is achieved through eliminating the transducer fixed electrode. Two M3-CMUT devices have been fabricated and their electrical impedances are compared. It is demonstrated that the 50 μm radius transducer without the fixed electrode shows a 70% increase in the membrane displacement amplitude at a DC voltage of 20 V compared with the M3-CMUT with a fixed bottom electrode of the same dimension.

Growth, Characterization and the Limits of Ultrathin Si0 2 Based Dielectrics for Future CMOS Applications (Invited)

ABSTRACT

International Electron Devices Meeting. Technical Digest (Cat. No.01CH37224)

In this paper we review recent progress in and outline the issues for high-K high-temperature (-1... more In this paper we review recent progress in and outline the issues for high-K high-temperature (-1000°C) poly-Si CMOS processes and devices and also demonstrate possible solutions. Specifically, we discuss device characteristics such as gate leakage currents, flatband voltage shifts, charge trapping, channel mobility, as well as integration and processing aspects. Results on a variety of high-K candidates including HfQ, A1203, Hf02/A1203, ZI-02, silicates, and AlN,(O,) deposited on silicon by different deposition techniques are shown to illustrate the complex issues for high-K dielectric integration into current Si technology.

Tungsten Gates using carbonyl chemistry: Electrical and processing properties as MOSFETs Gates

Symposium on VLSI Technology, 1997

ABSTRACT First Page of the Article

Method for etching chemically inert metal oxides

Apparatus and method for forming an oxynitride insulating layer on a semiconductor wafer

Capacitive micromachined ultrasonic transducer array with pencil beam shape and wide range beam steering

Oxynitride gate dielectric and method of forming

High-dielectric constant insulators for FEOL capacitors

Process options of forming silicided metal gates for advanced CMOS devices

Method of forming oxynitride gate dielectric

High mobility FETS using Al203 as a gate oxide

Ultrathin High-K Dielectrics Grown by Atomic Layer Deposition: A Comparative Study of ZrO2, Hf02, Y2O3 and Al203

Precursor source mixtures

International Technical Digest on Electron Devices Meeting, 1992

Very high transconductance 0.1 μm surface-channel pMOSFET devices are fabricated with p+-poly gat... more Very high transconductance 0.1 μm surface-channel pMOSFET devices are fabricated with p+-poly gate on 35 Å-thick gate oxide. A 600Å-deep p+ source-drain extension is used with self-aligned TiSi2 to achieve low device series resistance. The maximum saturation transconductances, 400 mS/mm at 300K and 500 mS/mm at 80K, are the highest reported to date for pMOSFET devices

Sensors and Actuators A: Physical, 2013

Abstract A linear array of capacitive micromachined ultrasonic transducer (CMUT) has been designe... more Abstract A linear array of capacitive micromachined ultrasonic transducer (CMUT) has been designed as an alternative to conventional piezoelectric transducers. The proposed array is favorable for imaging applications where there is a need for high resolution detection in directions with an angle other than that perpendicular to the axis of the transducer array. The transducer array cells include a thin silicon nitride membrane that is suspended over a bottom electrode, fabricated on a silicon wafer. In immersion mode, the transducer cell shape and dimensions are optimized for an operating frequency of 10 MHz. The proposed imager array is shown to be able to generate a pencil shape beam with a ∼1.5° half beam width for enhancing the detector resolution. A phased array technique is employed to excite multiple cells using time-delayed signals to steer the acoustic beam toward the object. Therefore, the need for mechanically moving the transducer array or the cell membrane is eliminated, which results in simplifying the transducer driving system. Moreover, unlike conventional transducers, the pencil beam can be effectively steered over a wide range of angles without producing grating lobes or degrading the power difference between the main lobe and side lobes. Consequently, in transmitting mode the power loss in any undesired directions is minimized and in receiving mode the noise level from other angles interfering with the data collection is suppressed, which improves the signal to noise ratio of the imager CMUT array.