M. Vrazel

The heterogeneous integration of optical interconnections into integrated microsystems

Emerging techniques for integrating optoelectronic (OE) devices, analog interface circuitry, RF circuitry, and digital logic into ultra-mixed signal systems offers approaches toward and demonstrations of integrated optical interconnections in electrical microsystems. As rising data rates dictate the use of optical interconnections and interfaces at increasingly smaller distances, optical interconnections stand at a threshold of opportunity for pervasive implementation if cost-effective integration process technology and performance can be implemented. Heterogeneous integration is one approach toward the integration of compound semiconductor OE devices, Si CMOS circuits, and organic materials. Heterogeneous integration approaches, which utilize dissimilar materials which can be independently grown and optimized, and are subsequently bonded together into an integrated system, are particularly attractive methods for creating high-performance microsystems. This paper describes a variety of optical interconnections integrated into microsystems using thin film heterogeneous integration. Thin film heterogeneous integration is attractive from the standpoint that the topography of the integrated microsystem can remain flat to within a few microns, substrates which are often optically absorbing are removed, both sides of the thin film devices can be processed (e.g., contacted, optically coated), and three-dimensionally stacked structures can be implemented. Demonstrations of interconnections using thin film heterogeneous integration technology include an integrated InGaAs/Si CMOS receiver circuit operating at 1 Gbps, an InGaAs thin film photodetector bonded onto a foundry Si CMOS microprocessor to demonstrate a single chip optically interconnected microprocessor, smart pixel emitter and detector arrays using resonant cavity enhanced P-i-N photodetectors bonded on top of per-pixel current controlled oscillators and resonant cavity enhanced light emitting diodes integrated onto digital to analog converter gray-scale per-pixel driver circuitry, and photodetectors embedded in waveguides on electrical interconnection substrates to demonstrate chip-to-chip embedded waveguide interconnections.

Realization of multigigabit channel equalization and crosstalk cancellation integrated circuits

In this paper, we present integrated circuit solutions that enable high-speed data transmission over legacy systems such as short reach optics and electrical backplanes. These circuits compensate for the most critical signal impairments, intersymbol interference and crosstalk. The finite impulse response (FIR) filter is the cornerstone of our architecture, and in this study we present 5- and 10-Gsym/s FIR filters in 2-/spl mu/m GaAs HBTs and 0.18-/spl mu/m CMOS, respectively. The GaAs FIR filter is used in conjunction with spectrally efficient four-level pulse-amplitude modulation to demonstrate 10-Gb/s data throughput over 150 m of 500 MHz/spl middot/km multimode fiber. The same filter is also used to demonstrate equalization and crosstalk cancellation at 5 Gb/s on legacy backplane. The crosstalk canceller improves the bit error rate by five orders of magnitude. Furthermore, our CMOS FIR filter is tested and demonstrates backplane channel equalization at 10 Gb/s. Finally, building blocks for crosstalk cancellation at 10 Gb/s are implemented in a 0.18-/spl mu/m CMOS process. These circuits will enable 10-Gb/s data rates on legacy systems.

Microsystem optoelectronic integration for mixed multisignal systems

The integration and packaging of optoelectronic devices with electronic circuits and systems has growing application in many fields, ranging from long to micro haul links. An exploration of the opportunities, integration technologies, and some recent results using thin-film device heterogeneous integration with Si CMOS VLSI and GaAs MESFET circuit technologies are presented. Applications explored include alignment tolerant optoelectronic links for network interconnections, smart pixel focal plane array processing through the integration of imaging arrays with sigma delta analog to digital converters underneath each pixel, and three-dimensional computational systems using vertical through-Si optical interconnections.

Planar lightwave integrated circuits with embedded actives for board and substrate level optical signal distribution

This paper explores design options for planar optical interconnections integrated onto boards, discusses fabrication options for both beam turning and embedded interconnections to optoelectronic devices, describes integration processes for creating embedded planar optical interconnections, and discusses measurement results for a number of integration schemes that have been demonstrated by the authors. In the area of optical interconnections with beams coupled to and from the board, the topics covered include integrated metal-coated polymer mirrors and volume holographic gratings for optical beam turning perpendicular to the board. Optical interconnections that utilize active thin film (approximately 1-5 /spl mu/m thick) optoelectronic components embedded in the board are also discussed, using both Si and high temperature FR-4 substrates. Both direct and evanescent coupling of optical signals into and out of the waveguide are discussed using embedded optical lasers and photodetectors.

A three-layer 3D silicon system using through-Si vertical optical interconnections and Si CMOS hybrid building blocks

We present for the first time a three-dimensional (3D) Si CMOS interconnection system consisting of three layers of optically interconnected hybrid integrated Si CMOS transceivers. The transceivers were fabricated using 0.8-/spl mu/m digital Si CMOS foundry circuits and were integrated with long wavelength InP-based emitters and detectors for through-Si vertical optical interconnections. The optical transmitter operated with a digital input and optical output with operation speeds up to 155 Mb/s. The optical receiver operated with an external optical input and a digital output up to 155 Mb/s. The transceivers were stacked to form 3D through-Si vertical optical interconnections and a fabricated three layer stack demonstrated optical interconnections between the three layers with operational speed of 1 Mb/s and bit-error rate of 10/sup -9/.

Highly alignment tolerant InGaAs inverted MSM photodetector heterogeneously integrated on a differential Si CMOS receiver operating at 1 Gbps

The increasing demand for high bandwidth, low latency I/O in gigascale systems is challenging current packaging technology. Optoelectronic I/O offers needed performance, but presents new challenges in mixed signal (digital, analog, optical, RF) design and test. In addition, the integration of OE interconnect must be suitable for high volume, low cost manufacturing of digital systems. This paper explores the heterogeneous integration of very large area, highly alignment tolerant photodetectors onto Si CMOS differential analog receiver circuits to realize noise-tolerant receiver interfaces for high-density interconnection electrical substrates with integrated optical links as well as for fiber optic links. The realization of an optically interconnected microprocessor that employs such a photodetector will also be discussed.

Analysis of alignment tolerant hybrid optoelectronic receivers for high density interconnection substrates

High frequency signal distribution in HDI/HDW substrates can be achieved using optical interconnections. To realize effective milli- and micro-haul interconnections on these substrates, the hybrid integration of independently optimized interface circuits and optoelectronic detectors is critical. Further, to realize effective cost goals, designing the optoelectronic interface for alignment tolerance is a key goal. This paper describes the design, fabrication, and test of hybrid integrated optoelectronic interface circuits designed for alignment tolerance and for integration onto an HDI/HDW substrate.

Hybrid optically interconnected microprocessor: an InP I-MSM integrated onto a mixed-signal CMOS analog optical receiver with a digital CMOS microprocessor

This paper presents the results of simultaneously working fully-differential optoelectronic receiver fabricated in Si CMOS with digital SIMD microprocessor on the same die next to analog, optical interface circuitry, the receiver have been hybrid integrated with a thin film InP-based inverted (I)-MSM photodetector and optically tested using external light source modulated by digital input signal. The noise immunity to mixed-signal digital switching noise of the differential receiver has been shown to be good enough to generate 10-9 BER.

Alignment tolerant hybrid photoreceivers using inverted MSMs

We report on the hybrid integration of a thin film large area (250/spl times/250 /spl mu/m/sup 2/, low capacitance (0.43 pF), high responsivity (0.5 A/W, with no AR coating) InGaAs/InP inverted-MSM onto a Si CMOS differential receiver circuit. This integrated receiver demonstrated a bit-error-rate of 10/sup -11/ at 414 Mbps and 0.1/spl times/10/sup -10/ at 480 Mbps. The alignment tolerance of this receiver has been modeled and measured at 200 Mbps, and the theoretical results correspond quite well to experimental data.

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.