Low temperature, low pressure CMOS compatible Cu -Cu thermo-compression bonding with Ti passivation for 3D IC integration

In this paper, we report the methodology of achieving low temperature, low pressure CMOS compatible Wafer-on-Wafer (WoW) Cu-Cu thermo-compression bonding using optimally chosen ultra-thin layer of Titanium (Ti) as a passivation layer. We systematically studied the effects of Ti thickness on bonding quality via its effects on surface roughness, oxidation prevention and inter diffusion of Cu. Through this study, we have found that a Ti thickness of 3 nm not only results in excellent bonding but also leads to a reduction in operating pressure to 2.5 bar and temperature to 175° C. The reduction in pressure is more than an order of magnitude lower relative to the current state-of-the-art. The lower operating pressure and temperature manifest themselves in a very good homogenous bond further highlighting the efficacy of our approach. Finally, our results have been corroborated by evidence from AFM study of the Cu/Ti surface prior to bonding. The bond strength of Cu-Cu as measured by Instron Microtester measurement system is found to be 190 MPa which compares very well with the reported literatures

Implementation of Static and Semi-Static Versions of a Bit-wise Pipelined Dual-rail NCL 2S Complement Multiplier

This paper focuses on implementing a 2s complement 8x8 dual-rail bit-wise pipelined multiplier using the asynchronous NULL Convention Logic (NCL) paradigm. The design utilizes a Wallace tree for partial product summation, and is implemented and simulated in VHDL, the transistor level, and the physical level, using a 1.8V 0.18,um TSMC CMOS process.The multiplier is realized using both static and semi-static Dualversions of the NCL gates; and these two implementations are compared in terms of area, power, and speed

Implementation of Static and Semi-Static Versions of a 24+8x8 Quad-rail NULL Convention Multiply and Accumulate Unit

This paper focuses on implementing a 2s complement 8x8 dual-rail bit-wise pipelined multiplier using the asynchronous null convention logic (NCL) paradigm. The design utilizes a Wallace tree for partial product summation, and is implemented and simulated in VHDL, the transistor level, and the physical level, using a 1.8V 0.18mum TSMC CMOS process. The multiplier is realized using both static and semi-static versions of the NCL gates; and these two implementations are compared in terms of area, power, and speed

Towards outperforming conventional sensor arrays with fabricated individual photonic vapour sensors inspired by Morpho butterflies.

Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tResearch Support, U.S. Gov't, Non-P.H.S.Combining vapour sensors into arrays is an accepted compromise to mitigate poor selectivity of conventional sensors. Here we show individual nanofabricated sensors that not only selectively detect separate vapours in pristine conditions but also quantify these vapours in mixtures, and when blended with a variable moisture background. Our sensor design is inspired by the iridescent nanostructure and gradient surface chemistry of Morpho butterflies and involves physical and chemical design criteria. The physical design involves optical interference and diffraction on the fabricated periodic nanostructures and uses optical loss in the nanostructure to enhance the spectral diversity of reflectance. The chemical design uses spatially controlled nanostructure functionalization. Thus, while quantitation of analytes in the presence of variable backgrounds is challenging for most sensor arrays, we achieve this goal using individual multivariable sensors. These colorimetric sensors can be tuned for numerous vapour sensing scenarios in confined areas or as individual nodes for distributed monitoring.We would like to acknowledge H. Ghiradella (University at Albany), M. Blohm and S. Duclos (GE) and V. Greanya, J. Abo-Shaeer, C. Nehl and M. Sandrock (DARPA) for fruitful discussions. This work has been supported in part from DARPA contract W911NF-10-C-0069 ‘Bio Inspired Photonics’ and from General Electric’s Advanced Technology research funds. The content of the information does not necessarily reflect the position or the policy of the US Government

Achieving of Intensified Conductive Interconnections for Flex-on-Flex by Using Metal Passivated Copper – Copper Thermocompression Bonding

There is a gradual increase in demand for flexible electronics due to the way it is going to empower the end user - to bent, roll/fold and arrange randomly in 3-D space, the devices without sacrificing the performance and reliability of devices, in a trend focused towards ever shrinking device footprint area. One of the prime mover towards realizing flexible electronics is interconnect scaling, which is motivating us to move towards three-dimensional interconnect integration. In this paper, we propose the interconnection of two flexible-flexible substrates by Thermocompression bonding between copper-to-copper, with their surface passivated with palladium, at low temperature and low pressure, to overcome the limitations imposed by conventional anisotropic conductive film (ACF) and nonconductive paste (NCP) approaches. The enhancement in interdiffusion of atomic species between the two surfaces, at low temperature and pressure, is possible only with unoxidized surface which has low RMS roughness or with surface which has varied film density. We have systematically optimized the thickness of palladium passivation layer for high quality Cu-Cu bonding, at low temperature of 140 oC and at low pressure of 5 bar. 2.06 nm RMS surface roughness was observed for Palladium passivation layer when its thickness was optimized at 5 nm, which made bonded Cu-Cu junction interface free from any copper oxide, as it was confirmed by X-ray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS) analysis. To confirm the quality of bonded interface, the samples were subjected to stress by folding just after Thermocompression bonding. Absence of any voids between the interfaces during Scanning Acoustic Microscopy (SAM) imaging confirms the superior quality of Cu-Cu bonding. The bonded interface image from cross-sectional Scanning Electron Microcopy (X-SEM) further reaffirms the quality of interface. Besides, very low contact resistance of ~2 E-7 ? - cm2 obtained for a fabricated daisy chain pattern with 70 um pitch and 100 um × 100 um bonding contact, in addition, confirms the good quality of bonding interface. The demonstrated bonding approach with metal passivated interconnect technique will be one of the prime contestant for future high bandwidth applications

Metal-Alloy Cu Surface Passivation Leads to High Quality Fine-Pitch Bump-Less Cu-Cu Bonding for 3D IC and Heterogeneous Integration Applications

In this paper, we report a low temperature, fine-pitch, bump-less, damascene compatible Cu-Cu thermocompression bonding, using an optimized ultra-thin passivation layer, Constantan, which is an alloy (Copper-Nickel) of 55% Cu and 45% Ni. Surface oxidation and its roughness are the major bottlenecks in achieving high quality, low temperature, and fine-pitch Cu-Cu bonding. In this endeavor, we have used Cu rich alloy (Constantan) for passivation of Cu surface prior to bonding. We have systematically optimized the constantan passivation layer thickness for high quality low temperature, low pressure, bump-less Cu-Cu bonding. Also, we have studied systematically the efficacy of Cu surface passivation with optimized ultra-thin constantan alloy passivation layer. After rigorous trial and optimization, we successfully identified 2 nm passivation layer thickness, at which very high quality Cu-Cu bonding could be accomplished at sub 200 °C with a nominal contact pressure of 0.4 MPa. Post-bonding, electrical and mechanical characterization were validated using four-probe IV measurement and bond strength measurement respectively. Furthermore, Cu-Cu bonding interface was analyzed using IR wafer bonder inspection tool. Very high bond strength of 163 MPa and defect free interface observed by WBI-IR clearly suggests, Cu-Cu finepitch bonding with optimized ultra-thin alloy of 2 nm thick constantan, is of very high quality and reliable. Moreover, this novel bonding approach with alloy based interconnect passivation technique is the prime contestant for future heterogeneous integration

Purification, characterization, and cloning of a bifunctional molybdoenzyme with hydratase and alcohol dehydrogenase activity

A bifunctional hydratase/alcohol dehydrogenase was isolated from the cyclohexanol degrading bacterium Alicycliphilus denitrificans DSMZ 14773. The enzyme catalyzes the addition of water to α,β-unsaturated carbonyl compounds and the subsequent alcohol oxidation. The purified enzyme showed three subunits in SDS gel, and the gene sequence revealed that this enzyme belongs to the molybdopterin binding oxidoreductase family containing molybdopterins, FAD, and iron-sulfur clusters