磷化铟微系统的制造挑战

Abstract

From the inception of Il-V microsystems, monolithically integrated device designs have beenthe motivating drive for this field, bringing together the utility of single-chip microsystemsand conventional fabrication techniques. Indium phosphide (InP) has a particular advantageof having a direct bandgap within the low loss telecommunication wavelength (1550 nm)range, able to support passive waveguiding and optical amplification, detection, and generationdepending on the exact alloy of In, P, As, Ga, or Al materials. Utilizing epitaxy, one canenvision the growth of a substrate that contains all of the components needed to establish asingle-chip optical microsystem, containing detectors, sources, waveguides, and mechanicalstructures. A monolithic InP MEMS system has, to our knowledge, yet to be realized due to thesignificant difficulties encountered when fabricating the integrated devices. In this paper wepresent our own research and consolidate findings from other research groups across the worldto give deeper insight into the practical aspects of InP monolithic microsystem development:epitaxial growth of InP-based alloys, etching techniques, common MEMS structures realized inInP, and future applications. We pay special attention to shedding light on considerations thatmust be taken when designing and fabricating a monolithic InP MEMS device.

1. Introduction

Il-V materials have long been studied for use in high performance electronic and optical systems. The maturation ofepitaxial growth techniques has allowed researchers to growcompound semiconductors with nearly arbitrary compositions, exhibiting widely variable mechanical and electricalproperties. The ability to dictate parameters such as the band-gap, refractive index, and etching selectivity of each individuallayer has broadened the scope and vision of researchers andexpanded the field of compound semiconductors into previ-ously unexplored territories.

The initial push for the use of compound semiconductorsstemmed from the very high electron mobilities, mean-freepaths and the direct-bandgap electronic structure possessedby Ill-V semiconductors over traditional silicon based tech-nologies [1]. Many authors have highlighted the high speedtransistor technologies made possible through the development ofInP-GaAs compound semiconductor epitaxy. Devicessuch as HEMTs [2], MODFETs [3], and integrated opticalreceivers/HEMTs(4] are made possible through the uniqueelectronic properties of M-V semiconductors.

In recent years, microelectromechanical systems (MEMMS)using InP-based materials have been investigated to augmentthese optical networks [7]. A number of examples have beenreported in literature of optical modulators, demultiplexers[8-13], and couplers [14, 15] all designed in Il-V materialsto facilitate monolithic integration of these optical components with photodetectors and sources. To our knowledge.there have not been any examples which have demonstratedfull monolithic integration of these MEMS components withtheir active optical elements (sources and detectors) for a variety of reasons. The goal of this review is to present relevantliterature related to InP MEMS devices and to discuss thechallenges that arise in developing integrated optical MEMSin these less-common materials. We have broken this paperinto sections which reflect the key investigations and devicesdeveloped in InP MEMS discussing the particular impact ofthe research on the InP MEMS community as a whole. It isour goal to shed light on the current state of the InP MEMSfield and provide an outlook for future investigations anddevice potential.