Stress analysis in 3D IC having Thermal Through Silicon Vias (TTSV)

TTSV is proposed for the removal of heat from between the IC layers as these TTSVs carries heat down to the sink. However, it may generate stress in Silicon. In the present paper, thermal-stress simulation of stack consists of three IC layers bonded face up is performed using finite element modeling tools. We also analyzed the stress generated in 3D IC containing TTSV. Further we proposed a method for lower stress around the TTSV. The method proposed decreases the Von Misses Stress by a value of 40Mpa on average considering all the IC layers. Thus by achieving this, functionality of the chip becomes more reliable

Possible large-N fixed-points and naturalness for O(N) scalar fields

We try to use scale-invariance and the large-N limit to find a non-trivial 4d O(N) scalar field model with controlled UV behavior and naturally light scalar excitations. The principle is to fix interactions by requiring the effective action for space-time dependent background fields to be finite and scale-invariant when regulators are removed. We find a line of non-trivial UV fixed-points in the large-N limit, parameterized by a dimensionless coupling. They reduce to classical la phi^4 theory when hbar -> 0. For hbar non-zero, neither action nor measure is scale-invariant, but the effective action is. Scale invariance makes it natural to set a mass deformation to zero. The model has phases where O(N) invariance is unbroken or spontaneously broken. Masses of the lightest excitations above the unbroken vacuum are found. We derive a non-linear equation for oscillations about the broken vacuum. The interaction potential is shown to have a locality property at large-N. In 3d, our construction reduces to the line of large-N fixed-points in |phi|^6 theory.Comment: 23 page

Efficient adaptive switch design for charge pumps in micro-scale energy harvesting

The performance of Micro-scale energy harvesting unit depends on the efficient design of charge-pump. Optimization of the dimension of MOSFET switches in charge pump is one of the techniques to improve the efficiency. In this work, a new optimization technique for transistor sizing and a concept of reconfigurable adaptive switches has been introduced to maximize the extracted power. A control unit is designed for adaptive reconfiguration of the switches. These proposed techniques are validated for linear charge-pump topology in UMC 180nm technology. Combined effect of size optimization of switch along with reconfigurable switch offers an improvement up to 23.5% in the net harvested power with 6% less silicon area

Carrier relaxation dynamics in defect states of epitaxial GaN/AlN/Si using ultrafast transient absorption spectroscopy

The relaxation dynamics of the carriers through the defect levels in an epitaxial GaN film grown with an AlN buffer layer on Si has been performed on the femto-picosecond timescale, using ultrafast transient absorption spectroscopy (UFTS). The sample was pumped above and below the band gap and probed with a white light continuum (480-800 nm). A combination of bi and triple exponential decay functions at different probe wavelengths were used to fit the kinetic profile of the carriers in the defect continuum. Based on the UFTS measurements, a model is proposed which explains the dynamics in the shallow traps and deep level defects. Furthermore, to determine the role of the lattice in the relaxation dynamics, the experiment was conducted at a low lattice temperature of 4.2 K. The relaxation constants from the UFTS measurements confirm not only the presence of shallow and deep level defects but also the involvement of phonons in one of the relaxation processes

Hybrid TTSV structure for heat mitigation and energy harvesting in 3D IC

Three Dimensional Integration seems to be one of the best candidates to overcome the various challenges and limitations faced by conventional planer integration. But, thermal issues related to this highly promising integration technique are the main bottleneck for wide scale application. This thermal issue threatens the further progress and development of the 3D IC. The best known possible way to reduce the heat generated within the integrated chip is cooling through the thermal through silicon via (TTSV). This work reports the utilization of time dependent fluctuation of temperature which is generated within the active layers of 3D IC. Pyroelectric effect of TTSV materials is used to convert the heat generated within 3D IC to electrical energy. 60K temperature fluctuation within the IC layer was used to convert as electrical energy and 9.89μW output power was observed. This paper reports the novelty of TTSV structure modification where TTSVs are used as simultaneous energy harvester and heat mitigator

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

Room temperature desorption of Self Assembled Monolayer from Copper surface for low temperature & low pressure thermocompression bonding

In this paper the utility of Self Assembled Monolayer (SAM) of Propanethiol (C3) for Copper protection from oxidation and subsequent desorption of the Thiol layer from Copper surface by using cold Helium plasma has been investigated. The major bottleneck of achieving low temperature and low pressure bonding is the presence of contamination and oxidation on the Copper surface. Use of Thiol can protect the freshly deposited Copper surface from oxidation and other contamination. Removal of this Thiol layer by Helium plasma just prior to bonding can bring down the required temperature of bonding to 200° and pressure to 4kN. This technique can open up a whole new platform for low temperature bonding for 3D ICs

Translational control of the SigR-directed oxidative stress response in streptomyces via IF3-mediated repression of a noncanonical GTC start codon

The major oxidative stress response in Streptomyces is controlled by the sigma factor SigR and its cognate antisigma factor RsrA, and SigR activity is tightly controlled through multiple mechanisms at both the transcriptional and posttranslational levels. Here we show that sigR has a highly unusual GTC start codon and that this leads to another level of SigR regulation, in which SigR translation is repressed by translation initiation factor 3 (IF3). Changing the GTC to a canonical start codon causes SigR to be overproduced relative to RsrA, resulting in unregulated and constitutive expression of the SigR regulon. Similarly, introducing IF3* mutations that impair its ability to repress SigR translation has the same effect. Thus, the noncanonical GTC sigR start codon and its repression by IF3 are critical for the correct and proper functioning of the oxidative stress regulatory system. sigR and rsrA are cotranscribed and translationally coupled, and it had therefore been assumed that SigR and RsrA are produced in stoichiometric amounts. Here we show that RsrA can be transcribed and translated independently of SigR, present evidence that RsrA is normally produced in excess of SigR, and describe the factors that determine SigR-RsrA stoichiometry.IMPORTANCE In all sigma factor-antisigma factor regulatory switches, the relative abundance of the two proteins is critical to the proper functioning of the system. Many sigma-antisigma operons are cotranscribed and translationally coupled, leading to a generic assumption that the sigma and antisigma factors are produced in a fixed 1:1 ratio. In the case of sigR-rsrA, we show instead that the antisigma factor is produced in excess over the sigma factor, providing a buffer to prevent spurious release of sigma activity. This excess arises in part because sigR has an extremely rare noncanonical GTC start codon, and as a result, SigR translation initiation is repressed by IF3. This finding highlights the potential significance of noncanonical start codons, very few of which have been characterized experimentally. It also emphasizes the limitations of predicting start codons using bioinformatic approaches, which rely heavily on the assumption that ATG, GTG, and TTG are the only permissible start codons

Facile synthesis and photoluminescence spectroscopy of 3D-triangular GaN nano prism islands

We report a strategy for fabrication of 3D triangular GaN nano prism islands (TGNPI) grown on Ga/Si(553) substrate at tow temperature by N-2(+) ions implantation using a sputtering gun technique. The annealing of Ga/Si(553) (600 degrees C) followed by nitridation (2 key) shows the formation of high quality GaN TGNPI cross-section. TGNPI morphology has been confirmed by atomic force microscopy. Furthermore, these nano prism islands exhibit prominent ultra-violet luminescence peaking at 366 nm upon 325 nm excitation wavelength along with a low intensity yellow luminescence broad peak at 545 nm which characterizes low defects density TGNPI. Furthermore, the time-resolved spectroscopy of luminescent TGNPI in nanoseconds holds promise for its futuristic application in next generation UV-based sensors as well as many portable optoelectronic devices

Tillage and Planting Density Affect the Performance of Maize Hybrids in Chitwan, Nepal

To find out whether the different tillage methods at different planting densities affect the performance of maize hybrids, an experiment was carried out at National Maize Research Program, Rampur during spring season of 2013 and 2014. The experiment was laid out in strip plot design with three replications having 12 treatments. The vertical factor was tillage with conservation tillage (No Tillage + residue=NT) and conventional tillage (CT) and the horizontal factor were genotypes (Rampur Hybrid-2 and RML-32/RML-17) and in split planting geometries (75cm × 25cm =53333 plants/ha, 70cm × 25cm=57142 plant/ha and 60cm ×25cm= 66666 plants/ha). In both the years, the highest number of cobs (73,177 and 67638/ha) was recorded at planting density of 66666/ha. NT had the highest no of kernel rows/cob (14.01) as against 12.12 in CT in 2014. The highest number of kernels (27.3 and 29.29) per row was recorded in NT during 2013 and 2014 respectively. Similarly, in 2014, the highest number of kernels were found in RML-32/RMl-17 (29.17/row) and planting density of 53333/ha (28.46/row). In 2013, RML-32/RML-17 produced the highest test weight of 363.94g over the Rampur hybrid-2 with 362.17g. Significantly the highest grain yield of 9240.00 kg/ha in 2013 and 7459.80 kg/ha in 2014 at planting geometry of 65cm ×25cm were recorded. No effects was found by tillage methods for grain yields of maize in 2013, but was found in 2014 (7012.18 kg in NT compared to 6037.59 kg/ha in CT). NT and wider spaced crop matured earlier in both the years; however Rampur hybrid-2 matured earlier to RML-32/RML-17 in 2013. In 2014, harvest index of 47.85 % was recorded in planting geometry of 66666/ha, the highest benefit cost ratio of 1.36 was worked out in NT and 1.46 at the density of 66666/ha. The highest value of 2.46% of soil organic matter was recorded in NT as compared to 2.43% in CT.Journal of Maize Research and Development (2015) 1(1):10-20DOI: http://dx.doi.org/10.5281/zenodo.3428