Thermomechanical reliability of copper-plated through-package vias (TPVs) in ultrathin bare glass interposers was investigated through modeling, design, fabrication, reliability characterization, and failure analysis. Finite-element models were developed to analyze stress and strain distribution in TPV structures, and to obtain design guidelines for reliable TPVs. In order to experimentally validate the predictions of simulations, bare glass substrates of 100 μm thickness with vias of 30 μm diameter at 120 μm pitch were metallized using Ti/Cu sputtering, followed by patterning and electroplating. Cu TPV daisy chains were fabricated and subjected to thermal cycling test between -55 °C and 125 °C to assess their thermomechanical reliability. Detailed cross-sectional analysis was also carried out by scanning electron microscope imaging of TPV cross sections. No electrical failures were detected in the Cu TPV chains. Failure analysis revealed copper delamination and crack formation in glass. The experimental reliability results are consistent with the thermomechanical models. Design and process recommendations are provided based on the modeling and experimental results.

This paper presents an analytical study on the use of deterministic chaos as an entropy source for the generation of random numbers. The chaotic signal generated by a phase-locked loop (PLL) device is investigated using numerical simulations. Depending on the system parameters, the chaos originating from the PLL device can be either bounded or unbounded in the phase direction. Bounded and unbounded chaos differs in terms of the flatness of the power spectrum associated with the chaotic signal. Random bits are generated by regular sampling of the signal from bounded and unbounded chaos. A white Gaussian noise source is also sampled regularly to generate random bits. By varying the sampling frequency, and based on the autocorrelation and the approximate entropy analysis of the resulting bit sequences, a comparison is made between bounded chaos, unbounded chaos and Gaussian white noise as an entropy source for random number generators.

This paper presents a random number generator (RNG) based on irregular sampling of regular waveform method where the irregular signal is obtained by combining Fibonacci-Galois ring oscillators with an XOR gate. The RNG is implemented on a FPGA (field-programmable gate array). The regular waveform generated by the digital clock manager of the FPGA, is sampled at times corresponding to certain number of rising edges of the irregular signal, and the resulting bit stream is subjected to statistical tests of randomness. It is demonstrated that the resulting bit sequence from the proposed RNG satisfies NIST 800-22 test suit and Rabbit and SmallCrush batteries from TestU01 library without any need for post-processing such as Von Neumann or XOR. A comparison between the methods regular sampling of irregular waveform and irregular sampling of regular waveform is given in terms of robustness against external interference. The impact of selection of Fibonacci-Galois polynomials is discussed. Using digital design flow for TSMC 65nm process, an asic implementation of the proposed RNG is given having 1115 gates and 4.811 mW estimated power.

This study presents the algebraic cryptanalysis of a continuous‐time chaotic random number generator (RNG) based on a Zhongtang chaotic system. The chaos‐based RNG provides key values for logic encryption, round key formation and the substitution box (S‐box) generation steps in AES (advanced encryption standard). In this study, an attack method is proposed to exploit the weaknesses of the chaos‐based RNG used in this cryptographic system. By observing a chaotic state variable and knowing the structure of the target RNG, output bit sequence of the target RNG is reproduced by a clone RNG used in master–slave synchronisation scheme. The feasibility of the attack system is confirmed through simulation and numerical results. Through this attack method, the same S‐box parameters and key values can be obtained which can be used for decryption of the proposed encryption algorithm. This study targets a specific continuous‐time chaos‐based RNG and the associated cryptographic system as a case study. However, the cryptanalysis method described in this study is applicable to any continuous‐time or discrete‐time chaos‐based RNGs. Therefore, this study highlights the security vulnerabilities of chaos‐based RNGs and emphasises that deterministic chaos phenomena itself should not be considered as the actual source of randomness.

Reliability of through-package vias (TPVs) in 100-μm glass, prefabricated with an innovative via-first process, is investigated through systematic modeling, design, fabrication, and reliability characterization. Finite element models were built to assess the impact of this novel process on stress and strain distribution in TPV structures. Thermomechanical simulations were carried out to provide design guidelines for reliable TPVs. In order to experimentally validate the predictions from simulations, test samples containing metallized TPVs with 60 μm diameter were fabricated with 100-μm thick glass. To assess the reliability of TPVs, daisy chains were fabricated and subjected to thermal cycling between -55 °C and 125 °C. TPV daisy chain resistances were measured at regular thermal cycling intervals to detect initiation of failures during reliability characterization. As predicted from mechanical modeling, changes in resistance were experimentally observed to be less than the chosen failure criterion, indicating no failures. Detailed mechanical failure analysis by scanning electron microscopy revealed elimination of delamination and crack failures in contrast to those observed in via-first bare glass interposers. This is attributed to the reduced stress and enhanced adhesion with the polymer layers.