Garrett Andrew Piech

Development of substrates for through glass vias (TGV) for 3DS-IC integration

Through-substrate vias (TSV) are critical for Three-Dimensional Stacked Integrated Circuits (3DS-IC) integration. While silicon traditionally has been used in this application, glass has properties that make it a very intriguing material for through substrate via applications. We note that the term glass describes a broad material set, with a wide range of properties driven by composition. For example, compositional changes allow tailoring of mechanical and thermal properties. Furthermore, novel forming processes available today enable reduction or elimination of time consuming and costly thinning or polishing processes, as well as opportunities to more easily scale the footprint of the substrate. Significant progress has been made to develop techniques to provide suitable through holes for vias in different glass compositions, which leverages the versatility of glass to create a substrate for TSV.

Coherent frequency-selective polarimeter for polarization-mode dispersion monitoring

Frequency-selective polarimeters measure the state of polarization of the individual spectral components of a modulated optical signal. They can be used either as stand-alone measuring devices or as parts of adaptive polarization-mode dispersion (PMD) compensators. This paper presents a novel frequency-selective polarimeter based on coherent detection, which has superior accuracy compared to previously proposed direct detection-based counterparts. This is due to the high-frequency resolution and power sensitivity of coherent detection, features that minimize the systematic and random error, respectively, in the measurement of the state of polarization of the individual spectral components of the received optical signal. The accuracy of the measurement is independent of the received signal bit rate and modulation format. The proposed frequency-selective polarimeter is studied both theoretically and experimentally. The primary theoretical contribution of this paper is a unified formalism, which allows the modeling of both direct and coherent detection-based frequency-selective polarimeters. Analytical expressions for the output signal of both types of frequency-selective polarimeters are derived. Based on these expressions, a common algorithm is proposed for the evaluation of the Stokes parameters. In addition, an example error signal is used as a metric in order to test the agreement of the theoretical model with the experimental measurements. The successful operation of the coherent frequency-selective polarimeter is demonstrated experimentally for a 10-Gb/s intensity-modulated nonreturn-to-zero (NRZ) optical signal in the presence of first-order polarization-mode dispersion. There is an excellent agreement between theory and experiment.

Fabrication of 3D-IC interposers

Over the past several years, the semiconductor industry has seen some tremendous developments in using glass as an interposer substrate. Glass has many properties that make it an ideal substrate for interposer substrates such as: ultra-high resistivity, low dielectric constant, ultra-low electrical loss and adjustable coefficient of thermal expansion (CTE) that allows management of 3D-IC stacks. Regardless of technical performance, any glass based solution must also provide significant cost advantages in substrate material, via formation, and subsequent processing. Cost-Effective Solutions In this paper, we will cover how fusion formed glass provides cost-effective solutions for the manufacturing of interposer materials for as-formed 100 μm precision substrate with a pristine surface, without the need for polishing, thus eliminating the manufacturing steps for polishing and thinning. Design Considerations For effective implementation of glass substrates, processing costs for through-glass-vias (TGV) on ultra-thin glass is also a challenge. This paper will reference data from several different designs to demonstrate the impact of design on Cornings TGV process cost relative to silicon solutions. It will also highlight processing lessons learned in fabricating TGV interposers from bare glass into complete packaged test vehicles and their impact on cost. Via Capabilities Furthermore, glasses via formation capabilities have dramatically improved over the past several months. Fully populated wafers with >100,000 through and blind holes (25 μm diameter) are fabricated today with 20μm diameters. We report on the significant enhancements demonstrated on important quality parameters. We will also report on strength parameters measured on TGV wafers and positive implications with respect to product reliability.

Glass interposer substrates: Fabrication, characterization and modeling

There is growing interest in applying glass as a substrate for 2.5D/3D applications. Glass has many material properties that make it well suited for interposer substrates. Glass based solutions provide significant opportunities for cost benefits by leveraging economies of scale as well as forming substrates at design thickness. A lot of work is being done to validate the value of glass as an interposer substrate. One important area is the electrical performance of glass relative to silicon. Because glass is an insulator, it is expected to have better electrical performance than silicon. Electrical characterization and electrical models demonstrate the advantages of the insulating properties of glass, and its positive impact on functional performance. Further advantages are anticipated in reliability performance, because of the ability to adjust thermal properties such as coefficient of thermal expansion (CTE) of glass. Modeling results demonstrating these improvements will be presented. Additionally, significant progress has been made in the demonstration of glass interposer fabrication. Fully patterned wafers and panels with through holes and blind holes are being fabricated today. Leveraging existing downstream processes for metallization on these substrates is also important for cost effectiveness and ease of transition into production. Progress on demonstrating the ability to leverage existing downstream processes to make functional glass interposers using both through and blind via technology will be presented.

Time-resolved performance analysis of a second-order PMD compensator

Design, test, and performance requirement and analysis for a polarization-mode-dispersion compensator (PMDC) with four degrees of freedom is presented. The performance is analyzed on the basis of time-integrated and time-resolved bit-error ratio (BER) measurements. Signal impairments are generated by both, first- and higher-order emulators. The probability distributions of bit errors measured over many one second intervals exhibit very long tails. Therefore even a PMDC with a good average BER performance may result in a significant total outage time for a given system.

Glass substrates for carrier and interposer applications and associated metrology solutions

Glass has many properties that make it an ideal substrate for important 3D-IC applications such as interposer substrates and glass carrier wafers. Critical material properties such as: ultra-high resistivity, low dielectric constant, ultra-low electrical loss and tailorable CTE, provide unique advantages. Forming processes such as the fusion forming process provide additional advantages around the ability to deliver low total thickness variation (TTV) without downstream grinding and polishing processes providing positive implications on both cost and performance. The ability to scale substrate sizes in size (450 mm wafers, panels) and thickness (down to 100 um) as well as panels provides tremendous advantages for the ability to scale for high volume manufacture. Just as important as being able to provide glass with these important attributes, is the ability to properly characterize them. We provide a summary highlighting the importance of the glass attributes in glass interposer and carrier applications, as well as implications of using the appropriate metrology solution to characterize them.

Wavelength tunable high-power single-mode 1060-nm DBR lasers

The wavelength tunable 1060-nm distributed Bragg reflector (DBR) laser chip consists of three sections: a gain section for lasing, and phase and DBR sections for wavelength control. A micro-heater is lithographically integrated on the top of the DBR section to tune the emission wavelength. The phase section is designed with either a top heater or by current injection to provide fine tuning of the wavelength. The wavelength tuning efficiency of our DBR laser is approximately 9 nm/W at the laser heat sink temperature of 25°C. Single-mode output powers of 686 mW and 605 mW were obtained at a CW gain drive current of 1.25 A and heat sink temperatures of 25°C and 60°C, respectively. Gain-switching by applying 1.1 GHz sinusoidal signal mixed with 600 mA DC injection current produced approximately 58 ps long optical pulses with 3.1 W peak power and 228 mW average power. The average power increased to 267 mW and pulse width broadened to 70 ps with DC bias of 700 mA. In CW operation, one of the applications for high-power single-mode DBR lasers is for non-linear frequency conversion. The light emitted from the 1060-nm DBR laser chip was coupled into a single-mode periodically poled lithium niobate (PPLN) crystal waveguide. Up to 350 mW optical power at 530 nm with the wall-plug efficiency of up to 15% was demonstrated.

350 mW green light emission from a directly frequency-doubled DBR laser in a compact package

We report a compact green light source consisting of a 1060-nm DBR laser, a periodically poled lithium niobate crystal waveguide and an adaptive optic element consisting of a micro-electro-mechanical system actuator. Up to 350 mW optical power at 530 nm with the wallplug efficiency of up to 15% was demonstrated. The change in the optical power at constant current over the temperature range from 10°C to 70°C was less than 18%.