Sa Huang

Heterogeneous materials integration: compliant substrates to active device and materials packaging

The drive for the heterogeneous integration of materials has led to significant advances in materials and device processing, and in the understanding of defect production and control during epitaxy. Heterogeneous integration is driven by microelectronic and packaging trends, and the advent of new materials, such as GaN, that do not possess native substrates. During the last decade, these objectives led to research in the development of compliant substrates. While the ideal compliant substrate concept and implementation may be flawed, this research has certainly advanced materials integration technology. This paper will provide an overview of recent results in compliant substrate experiments and interpretation, and the related advancement of materials and device integration and packaging deriving from some of this research.

GaN metal–semiconductor–metal photodetectors grown on lithium gallate substrates by molecular-beam epitaxy

The growth, fabrication, and characterization of ultraviolet metal–semiconductor–metal (MSM) GaN photodetectors grown on LiGaO2 by molecular-beam epitaxy are reported herein. GaN/LiGaO2 material with dislocation densities of approximately 108 cm−2 and x-ray diffraction (00.4) full width at half maximum of 75 arcsec results in MSMs showing high responsivity, 0.105 A/W, at a reverse bias voltage of 20 V at 308 nm, and low dark currents of 7.88 pA at a 60 V reverse bias. Given the etch selectivity of the GaN/LiGaO2 system and the excellent performance of these devices, GaN device integration onto alternative substrates appears promising.

High-speed large-area inverted InGaAs thin-film metal-semiconductor-metal photodetectors

Inverted metal-semiconductor-metal (I-MSM) photodetectors, which are thin-film MSMs with the growth substrate removed and fingers on the bottom of the device (to eliminate finger shadowing to enhance responsivity), are reported herein for high-speed high-efficiency large-area photodetectors. Reported herein are the highest speed vertically addressed large-area (40-/spl mu/m diameter) photodetectors reported to date, which operate with a responsivity of 0.16 A/W and a full-width half-maximum of less than 5 ps. Materials, fabrication processes, heterogeneous integration, and characterization of I-MSM photodetectors are presented in this paper, as measured using a fiber-based electrooptic sampling system. These large-area photodetectors are ideal for vertically addressed high-speed optical links which need alignment-tolerant packaging for cost sensitive applications.

The heterogenous integration of GaN thin-film metal-semiconductor-metal photodetectors onto silicon

The heterogeneous integration of GaN thin-film metal-semiconductor-metal (MSM) photodetectors onto a host substrate of SiO/sub 2/-Si is reported. Thin-film GaN photodetectors were separated from the lithium gallate (LiGaO/sub 2/) growth substrate using selective etching, and contact bonded onto a SiO/sub 2/-Si host substrate. The thin-film MSMs exhibited a dark current of 13.36 pA and an UV photoresponse at 308 nm of 0.11 A/W at a reverse bias voltage of 20 V. This first demonstration of GaN thin-film device integration onto SiO/sub 2/-Si using a low-temperature integration process, combined with the advances in GaN material quality on LiGaO/sub 2/ substrates, enables the integration of GaN devices with Si circuitry for heterogeneously integrated systems.

Recent advances in III-nitride devices grown on lithium gallate

Recent advances in the growth of III-nitride materials and devices include: (i) The reduction of the near-surface threading dislocation density in GaN on lithium gallate (LGO) to 2 × 10 7 cm -2 . (ii) The demonstration of GaN, 50 × 130 μm, metal-semiconductor-metal (MSM) photodiodes with extremely low leakage current, 0.11 pA at 2 V and 7.9 pA at 60 V, and UV photoresponse at 308 nm and 20 V of 0.105 A/W. (iii) State of the art MSM devices have been successfully removed from the LGO substrate and attached to silicon wafers with no degradation in current characteristics. (iv) Demonstration of very thin, 0.7 μm HFET structures, grown at a rapid rate of 0.9 μm/h, with near state of the art room temperature 2DEG mobilities of 1365 cm 2 /Vs at a sheet charge of 9 x 10 12 cm -2 . (v) The elimination of substrate impurity diffusion by inclusion of gettering buffers has also been demonstrated.

Design of a smart pixel multispectral imaging array using 3D stacked thin film detectors on Si CMOS circuits

We discuss the design of a smart multispectral imaging system which can be fabricated with independently optimized detector arrays and Si CMOS circuits, which are stacked in three dimensions on top of one another for complete physical registration of the multispectral image. This smart multispectral imager utilizes the heterogeneous integration of thin film GaN (UV), MCT (MWIR), and Si CMOS circuitry to create an outstanding example of the power of heterogeneous integration for enhancing optical systems using electronic signal processing capabilities.

A 10 Gbit/s Si CMOS transimpedance amplifier with an integrated MSM photodetector for optical interconnections

A wideband preamplifier is designed and fabricated using a 0.18 /spl mu/m CMOS technology. The amplifier is heterogeneously integrated with a thin film InGaAs inverted MSM photodetector, and a successful demonstration at a bit rate of 10 Gbps is reported.

Heterogeneous integration: from substrate technology to active packaging

Heterogeneous integration of dissimilar materials and devices is necessary for the continued advancement of electronic and optoelectronic systems. A range of processes has been developed in recent years that will enable system integration and advanced packaging. Herein, we outline our approaches towards heterogeneous integration.

Thin film GaN metal-semiconductor-metal photodetectors integrated onto silicon

Summary form only given. In this paper, metal-semiconductor-metal (MSM) photodetector dark current and responsivity results for the growth of GaN on lithium gallate (LiGaO/sub 2/) substrates is reported, as well as the heterogeneous integration of thin film GaN MSM detectors onto host substrates.

GaN thin film material bonded to host substrates using selective chemical etching

We report on an approach toward GaN thin film separation and integration on dissimilar materials. To achieve the separation of thin film GaN, a LiGaO/sub 2/ substrate is used for the GaN growth substrate. LiGaO/sub 2/ is a promising substrate for high quality GaN growth, demonstrating good dislocation densities compared to GaN grown on sapphire.