Saurabh K. Lohokare

Electrical characterization of flip-chip interconnects formed using a novel conductive-adhesive-based process

Using conventional microfabrication techniques, we have developed a new, low-cost wafer bumping process that enables a high degree of control over patterning of conductive adhesive interconnects. This approach obviates the need for development of dispensing and scraping head equipment that may otherwise be required for mass fabrication of lithographically patterned adhesive bumps. Flip-chip interconnects formed using this new process offer better electrical performance as compared to those formed by squeegee-based definition techniques. This is inferred in this paper by experimentally demonstrating lower contact resistance with the polished bumps as compared to the squeegeed bumps. Furthermore, in order to study the high-speed electrical performance characteristics of these conductive adhesive bumps, a 10-GHz 1.55-mum p-i-n photodetector fabricated in the antimonide material system was used as case study. The results from the bandwidth characterization of the polymer flip-chip-integrated detector showed minimum degradation in the high-speed performance characteristics of the detector

Integrated optoelectronic transmitter and receiver multi-chip modules for three-dimensional chip-level micro-optical interconnects

We demonstrate a chip-scale micro-optical interconnect. The prototype system for this demonstration consists of optoelectronic transmitter and receiver multichip modules. A diffractive optical element (DOE) is used for optically interconnecting the multichip modules and in establishing a point-to-point link. The link length, as measured from the optical source of the transmitter to the detector plane of the receiver, is only 2.332 mm. The transmitter and receiver module dimensions as well as the integrated system volume are comparable to very large scale integration (VLSI). The design, fabrication, integration of this system, and experimental results are presented.

High fill-factor avalanche photodetectors for near-infrared free-space photonic networks

Diffractive optical elements (DOEs) offer the ability to boost fill factors of high-speed (field-of-view limited) near-infrared detectors. In this context, we have investigated the design and fabrication of a system that involves integration of DOEs with avalanche photodetectors (APDs). These APDs are implemented in the antimonide material system for op- eration around a 2.1-mm wavelength. Consequently, such systems could be used to reduce the required threshold power at free-space photonic receivers. To this end, we present the design and fabrication technolo- gies for the DOEs, APDs, and their integration using polymer-based flip- chip interconnections.

Integrated micro-optical multichip module based on uncooled InGaAsSb/AlGaAsSb detector for noninvasive glucose monitoring using NIR absorption spectroscopy

The 2-2.5μm region of the electromagnetic spectrum is of particular importance for the non-invasive monitoring of blood glucose using absorption spectroscopy, since it can provide the strongest signature as compared to other water transmission windows. Currently available spectroscopy systems for this application require high-gain and low-noise detectors in order to achieve sufficient signal-to-noise ratio measurements. In this context, we are investigating the integration of micro-optics along with InGaAsSb/AlGaAsSb avalanche photodetectors in order to demonstrate high-fill factor, high quantum efficiency and eventually the ability to evaluate the blood glucose concentration with high accuracy. Also, using the bandgap engineering options afforded by the quaternary antimonide structures, the spectral response of the detector can be tuned over this wavelength range. In this paper, we present the design, fabrication and integration of the multi-chip modules, the constituent technologies required to realize them and experimental results from their characterization.

Integrated 3D micro-optical interconnection system

Integrated 3-D Micro-Optical Interconnection System Chip-level optical interconnects is an alternative technology that offers the ability to potentially overcome the interconnect bottleneck projected to occur in high-end computing and telecommunication systems. In this context, we are investigating a fused 3-D micro-optical architecture that enables through-wafer vertical optical interconnects. Based on this architecture a prototype 3-D micro-optical interconnection system is fabricated that is scaleable and can be easily modified to implement various optical interconnect configurations. This prototype consists of an integrated optoelectronic transmitter and receiver multichip module. A diffractive optical element is used for optically interconnecting the multichip modules and in establishing a point-to-point link. The link length, as measured from the optical source of the transmitter to the detector plane of the receiver is 2.332 mm. The transmitter and receiver module dimensions as well as the integrated system volume are a meager 2.9x3.3 mm2, 2.1x2.7 mm2, and 15.27mm3, respectively, and preserve the VLSI-scale. The design, fabrication, integration of this system, and experimental results are presented.

Integrated micro-optical multichip module based on an uncooled InGaAsSb∕AlGaAsSb photodetector

This paper focuses on the integration of InGaAsSb photodetectors along with micro-optics in order to realize a prototype system that can achieve a stronger response during atmospheric profiling and spectroscopy measurements. The integration of the detector was executed using a novel conductive-adhesive-based flip-chip integration process. The design, fabrication, and integration of the constituent technologies and experimental results from their characterization are presented.

Polymer Flip-Chip Integrated, AlGaAsSb/AlGaSb p-i-n Photodetectors For 1550 nm High-Speed Optical Interconnects

AlGaAsSb/AlGaSb heterostructures offer the ability to realize high-performance devices for 1550 nm high-speed optical interconnect applications. In this context, we present the design, fabrication, integration and characterization of 10 GHz p-i-n photodetectors in this material system. This effort has involved an investigation into inductively coupled plasma (ICP) etching of these materials and the development of a novel process for their conductive polymer based flip chip die attach.

10-Gbytes/s, three-dimensional parallel optical interconnects using a novel conductive polymer flip-chip process

Micro-optics offers the ability to realize massively parallel, surface-normal interconnects at the chip scale. In this context, we investigate the integration of a 10-Gbytes/s, 850-nm vertical-cavity surface-emitting laser (VCSEL) with a 2×2 array of continuous surface profile, diffractive optical elements to demonstrate a prototype system that incorporates 3-D, highly dense, parallel optical interconnects. The integration is achieved using a novel conductive polymer-based flip-chip process, which is implemented using conventional fabrication techniques. We present experimental results from the design, fabrication, integration, and characterization of the prototype system.