Kenneth P. Roenker

Flip-chip packaging using micromachined conductive polymer bumps and alignment pedestals for MOEMS

Using flip-chip bonding techniques with micromachined conductive polymer bumps and passive alignment techniques with electroplated side alignment pedestal bumps, a prototype microoptoelectromechanical systems (MOEMS) structure for optical input/output (I/O) couplers has been designed, fabricated and characterized. A top MOEMS substrate has through holes, contact metal pads, and side alignment pedestals with electroplated NiFe to align GaAs metal-semiconductor-metals (MSMs). Conductive polymer bumps have been formed on contact metal pads of GaAs MSMs using thick photoresist bump-holes as molding patterns. A diced GaAs photodetectors die with micromachined conductive polymer bumps was aligned to the side alignment pedestals and flip-chip bonded onto the substrate. This conductive polymer flip-chip bonding technique allowed a very low contact resistance (/spl sim/10 m/spl Omega/), a lower bonding temperature (/spl sim/170/spl deg/C), and simple processing steps. The GaAs MSM photodetectors flip-chip mounted on the top of OE-MCM substrate showed a low dark current of about 10 nA and a high responsivity of 0.33 A/W.

Performance enhancement of GaInP/GaAs heterojunction bipolar phototransistors using dc base bias

GaInP-GaAs heterojunction bipolar phototransistors grown by metal organic vapor phase epitaxy (MOVPE) and operated with frontside optical injection through the emitter are reported with high optical gain (<88) and record high frequency performance (28 GHz). Heteropassivation of the extrinsic base surface is employed using a depleted GaInP emitter layer between the nonself-aligned base contact and the emitter mesa. The phototransistors performance is shown to improve with increasing dc base bias in agreement with predictions of a recently reported Gummel-Poon model. Experimental results are reported for devices with optical active areas of 10/spl times/10 /spl mu/m/sup 2/, 20/spl times/20 /spl mu/m/sup 2/, and 30/spl times/30 /spl mu/m/sup 2/, with peak measured cutoff frequencies of 28.5, 23.1, and 18.5 GHz, respectively, obtained at collector current densities between 2/spl times/10/sup 3/ and 6/spl times/10/sup 3/ A/cm/sup 2/.

Gummel–Poon model for Npn heterojunction bipolar phototransistors

A Gummel–Poon model for abrupt, single heterojunction Npn bipolar phototransistors is described including the effects of the dc base bias on the current and optical gains. Initially, the excess electron concentration at the emitter end of the quasineutral base is determined by matching the thermionic field emission across the emitter–base heterojunction with the diffusion current at the emitter end of the base and including the effects of optical generation. The result is used in determining the electron profile in the base from which the base charge and the electron component to the emitter and collector currents are calculated following the Gummel–Poon model. The photocurrent’s components due to optical absorption in the quasineutral base, the base–collector space charge region, and the collector region are determined taking into account the nonuniform optical generation assuming topside illumination. A comprehensive description of the recombination current components is incorporated including the effec...

An analytical model for SiC MESFETs

An improved analytical model for simulating the performance of SiC MESFETs has been developed for use in device design for high frequency, high power applications. The model is based on a two-dimensional analysis of the charge distribution under the gate and incorporates a field-dependent mobility, velocity saturation and charge buildup in the channel. The model is used to generate the large signal current-voltage characteristics of the device and transconductance, output conductance and capacitances for a small signal model.

Refinements in the method of moments for analysis of multiexponential capacitance transients in deep‐level transient spectroscopy

The analysis of multiexponential capacitance transients that arise in deep‐level transient spectroscopy has been examined. The method of moments, a technique that provides a reliable method for resolution of a multiexponential capacitance transient into its exponential components, has been adapted and enhanced by incorporating an initial fast Fourier transform to extract the base‐line offset, and a refinement in the cutoff correction to the moments integrals which improves convergence and accuracy. In addition, the mean displaced ratio smoothing algorithm has been incorporated and shown to improve the method’s accuracy in the presence of noise. For the case where the response is not significantly convoluted with the excitation, a simplified form of the method of moments technique provides a simple and more direct determination of the exponential components. Examples of results for simulated data are provided illustrating application of the analysis. The limitations of the technique in determining the numb...

Design of a InP/In1−xGaxAsyP1−y/In0.53Ga0.47As emitter-base junction in a Pnp heterojunction bipolar transistor for increased hole injection efficiency

Starting with Burt’s envelope function theory, we calculate the transmission coefficients of holes across an InP/In1−xGaxAsyP1−y/In0.53Ga0.47As heterointerface while varying the width and gallium and arsenic fractions of the InP lattice-matched quaternary compound (x=0.47y). While comparing our results to the case of an abrupt InP/In0.53Ga0.47As interface, we find that the transmission coefficients of both heavy- and light-holes can be enhanced significantly for a 60-A-wide quaternary layer with an arsenic fraction y=0.4 (x=0.188). This should lead to an enhanced hole injection efficiency of Pnp heterojunction bipolar transistors using the heterointerface analyzed here as an improved design of the emitter-base junction.

A thermionic-field-diffusion model for Npn bipolar heterojunction phototransistors

This article describes the development of a thermionic-field-diffusion model for use in the analysis and design of abrupt, single heterojunction bipolar phototransistors (HPTs) for use in HBT-based optical receivers. In particular, included in this approach are the effects of a dc base bias on the optical gain and device performance. Taking into account the optical generation, the excess electron concentration at the emitter end of the quasi-neutral base is initially determined using a matching of the thermionic field emission across the emitter-base heterojunction with the diffusion current at the emitter end of the base. At the collector end of the base region, a finite electron concentration is used based on the collector current density. The results are used to determine the electron profile in the quasi-neutral base region and the diffusion components to the emitter and collector currents. To determine the device’s optical gain, the photocurrent and the small signal current gain are calculated. The d...

Simulation of PNP InAlAs/InGaAs heterojunction bipolar transistors

The performance of single heterojunction InAlAs/InGaAs PNP heterojunction bipolar transistors is modeled numerically and good agreement is found with experimental measurements. Peak experimental values of f/sub T/=14 GHz, f/sub Max/=22 GHz, /spl beta/=170 and U=38 dB are obtained near a collector current density of 10/sup 4/ A/cm/sup 2/ for a nonoptimized device.

A thermionic-emission-diffusion model for graded base Pnp heterojunction bipolar transistors

An analytical model which matches thermionic-emission-diffusion of holes across the emitter-base heterojunction with drift-diffusion transport across a graded base has been developed and used to examine the performance capabilities of InP-based Pnp heterojunction bipolar transistors (HBTs). Hole drift-diffusion across the emitter-base space charge region is shown to be of comparable importance to thermionic emission in controlling hole injection into the base. The effects of compositional base grading on the recombination currents is also taken into account. Compositional grading of the base is shown to enhance the device’s current gain by as much as a factor of 10 by reducing recombination in the quasi-neutral base. More importantly, compositional base grading significantly reduces the base transit time which improves the device’s peak cutoff frequency by as much as a factor of 1.5. A cutoff frequency as high as 35 GHz is found to be possible. The analysis indicates that composition grading of the base c...

Implications of hole vs electron transport properties for high speed Pnp heterojunction bipolar transistors

Abstract This paper examines the implications of differences in hole and electron transport properties on the microwave performance potential of InP-based Pnp HBTs. In particular, the carrier mobility, diffusion length, saturation velocity and ballistic transport properties for holes vs electrons are compared and their implications for Pnp device performance, such as the current gain and high frequency performance. The effects of the doping level on the mobility and minority carrier lifetime are included using empirical models fit to the available experimental data. The results show that, while the holes transport properties are inferior to those for the electron, the minority carrier lifetime is larger for holes than electrons so that the hole diffusion length in the base is smaller but comparable to the electrons. As a result, Pnp HBTs with adequate current gain can be achieved with only a modest reduction in the base width compared with the Npn. For the devices microwave performance, the holes characteristics determine the base transit time and the collector delay time, which limit the Pnp HBTs high frequency performance.