Scott A. Merritt

Electroless remetallization of aluminum bond pads on CMOS driver chip for flip-chip attachment to vertical cavity surface emitting lasers (VCSEL's)

A method for remetallizing the bond pads of electronic chips, which are initially metallized with aluminum or aluminum alloy is presented. Application of electroless plating process for the remetallization of aluminum to a solderable gold surface can reduce the cost and complication of the widely accepted flip-chip interconnection technology. We have developed a step by step nickel/gold wafer bumping technique (remetallized bump height is 5.0 /spl mu/m) for the appropriate solder (15.0 /spl mu/m of In:Pb). Variation of roughness of the remetallized surface has been studied carefully. We have completed prototype research studies on test devices and successfully packaged the flip-chip bonded hybrid pair of a CMOS driver chip and a dummy structure of vertical cavity surface emitting laser (VCSEL) array. Cross section of the flip-chip solder joint is studied. Also, adhesion strength of the metal deposit is investigated.

Automated estimation of implicit time and amplitude from the flicker electroretinogram.

The electroretinogram (ERG) has been shown to yield sensitive and specific information about the development of neovascularization in ischemic disorders such as diabetic retinopathy and central retinal vein occlusion. However, even though the test is quick, easy to perform, and carries few risks, the ERG is poorly utilized in clinical situations because of the extended training period necessary for test interpretation. We have developed an algorithm that estimates the phase and amplitude of a 30-Hz flicker ERG and that is relatively insensitive to many forms of interference in ERG recordings. These estimates can be directly compared to established criteria for the risk of proliferative retinal disease.

Measurement of the facet modal reflectivity spectrum in high quality semiconductor traveling wave amplifiers

We demonstrate that the Hakki-Paoli technique, commonly used for measuring single pass gain in semiconductor lasers, can be modified to measure facet modal reflectivity down to 10/sup -6/ in semiconductor laser amplifiers. We also introduce a new technique based on Fourier and Hilbert transformations of the spontaneous emission spectrum (the SET method) which enhances the signal-to-noise ratio and permits modal reflectivity measurements down to 10/sup -1/. >

Etch Characteristics of Succinic Acid/Ammonia/Hydrogen Peroxide versus Aluminum Mole Fraction in AlGaAs

We have measured the etch rate and selectivity of succinic acid/ammonia/hydrogen peroxide etchants on Al x Ga 1-x As with aluminum mole fractions of 0.1, 0.2, 0.4, and 0.6. The sensitivity to pH, peroxide concentration, and temperature was studied in a regime appropriate for fabricating GaAs/AlGaAs optoelectronic devices. The selectivity between Al 0.2 Ga 0.8 As and Al 0.4 Ga 0.6 As increases monotonically over the range of pH studied and is greater than 150 at pH 5.3. These results indicate aluminum mole fractions as low as 40% can be used for etch stop layers in GaAs/AlGaAs

GaAs-AlGaAs QW diluted waveguide laser with low-loss, alignment-tolerant coupling to a single-mode fiber

We report on low-loss, alignment-tolerant coupling between a single-quantum-well (SQW) GaAs-AlGaAs laser and a cleaved single-mode fiber. The laser was fabricated using conventional growth and processing techniques, and did not involve any regrowth. The mode size in the transverse direction was expanded by using a diluted waveguide structure. A butt-coupling efficiency of 66% was achieved against a theoretically possible 78% (which does not correct for Fresnel losses). In addition, large alignment tolerances for a 1-dB excess loss of /spl plusmn/2.0 pm and /spl plusmn/1.0 /spl mu/m were measured in the lateral and the transverse directions, respectively.

Polarization insensitive 1.55-μm optical amplifier with GaAs delta-strained Ga/sub 0.47/In/sub 0.53/As quantum wells

We report a novel, polarization insensitive, 1.55-/spl mu/m semiconductor optical amplifier grown by solid source molecular beam epitaxy. The active region contains six Ga/sub 0.47/In/sub 0.53/As quantum wells, each containing three tensile strained GaAs delta layers. Simple ridge waveguide devices were fabricated with 8/spl deg/ angled facets. The internal gain is 26.5 dB for both the transverse electric and transverse magnetic polarizations at a wavelength of 1.55 /spl mu/m and an injection current of 375 mA. The polarization sensitivity of the gain is less than 1 dB for a bandwidth of 45 nm, and the gain is nearly flat with a variation of less than 1 dB for a bandwidth of 20 nm. The saturation output power of these devices is 11 dBm. These results are reproducible and comparable to reports from more complex device designs.

A low-cost electroless plating method for producing flip-chip bondable and wire-bondable circuit pads for smart pixel application

We have developed and optimized a step-by-step electroless re-metallization process for aluminum that can reduce the cost and complication of substrate preparation for flip-chip microassembly. Our current effort is to utilize the same electroless plating process to coat optical fibers with a solderable nickel/gold layer, to make them suitable for silicon waferboard integration.

Half-watt high-power single mode superluminescent LED at 1335 nm with single-facet electro-optical efficiency of 28%

We report on half-Watt level single spatial mode superluminescent laser diode at 1335 nm. Output optical power in excess of 500 mW from a single facet of angle-striped waveguide was realized at 10°C of heatsink temperature with peak electro-optical efficiency of 28%. To our knowledge this is the highest optical power and electro-optic conversion efficiency in a SLED device reported so far in the literature. Further optimization could lead to revolutionary result: 1) the creation of a high power optical device (SLED) with electro-optical efficiencies approaching and/or exceeding that of Fabry-Perot lasers (counting both facet outputs) with absolute optical power levels compared to that of Fabry-Perot lasers, 2) Electro-optical efficiencies approaching internal quantum efficiencies which could well exceed the 70-80% range observed in present commercial semiconductor laser and light-emitting structures.

Wet-chemistry surface treatment for dark-current reduction that preserves lateral dimensions of reactive ion etched Ga/sub 0.47/In/sub 0.53/As p-i-n diode photodetectors

A wet-chemistry treatment, consisting of a fresh mixture of one-to-one 2-propanol plus concentrated sulfuric acid added to photoresist developer, which is tetramethyl ammonium hydroxide, was found to reduce the dark-current density at the -5-V dc reverse-bias to 2 pA//spl mu/m/sup 2/ (2/spl times/10/sup -4/ A/cm/sup 2/), and simultaneously to maintain the lateral geometrical dimensions, of reactive ion etched, 3 micrometer tall, right-cylinder mesa, Ga/sub 0.47/In/sub 0.53/As p-i-n diode photodetectors with diameters of 100, 50, and 25 /spl mu/m.

Alignment-tolerant lasers and silicon waferboard integration

Intrinsically large mode semiconductor lasers and mode transformers monolithically integrated with semiconductor lasers, are two promising approaches for making alignment tolerant structures that can be used for passive alignment to single mode optical fibers. This technique, in conjunction with a recently developed silicon waferboard integration scheme, will significantly simplify the assembly process and the packaging of transmitter laser arrays. The passive alignment technique consists of octagonal electrodeposited copper bosses to physically register the laser chip with percussion etched inverted pyramidal receptacles and v-grooves in a silicon substrate.