Scan-based design for test (DFT) is a powerful testing scheme, but it can be used to retrieve the secrets stored in a crypto chip, thus compromising its security. On one hand, sacrificing the security for testability by using a traditional scan-based DFT restricts its use in privacy sensitive applications. On the other hand, sacrificing the testability for security by abandoning the scan-based DFT hurts the product quality. The security of a crypto chip comes from the small secret key stored in a few registers, and the testability of a crypto chip comes from the data path and control path implementing the crypto algorithm. Based on this key observation, the authors propose a novel scan DFT architecture called secure scan that maintains the high test quality of traditional scan DFT without compromising the security. They used a hardware implementation of the advanced encryption standard to show that the traditional scan DFT scheme can compromise the secret key. They then showed that by using secure-scan DFT, neither the secret key nor the testability of the AES implementation is compromised

A 2.45 GHz microwave-plasma chemical-vapor deposition (MPCVD) reactor was designed and built in-house by collaborating with Guangdong TrueOne Semiconductor Technology Co., Ltd. A cylindrical cavity was designed as the deposition chamber and a circumferential coaxial-mode transformer located at the top of the cavity was adopted as the antenna. Two quartz-ring windows that were placed far away from the plasma and cooled by water-cooling cavity walls were used to affix the antenna to the cavity and act as a vacuum seal for the reactor, respectively. This design improved the sealing and protected the quartz windows. In addition, a numerical simulation was proposed to predict the electric-field and plasma-density distributions in the cavity. Based on the simulation results, a microwave-plasma reactor with TM₀₂₁ mode was built. The leak rate of this new reactor was tested to be as low as 1 × 10⁻⁸ Pa·m³·s⁻¹, and the maximal microwave power was as high as 10 kW. Then, single-crystal diamond films were grown with the morphology and crystalline quality characterized by an optical microscope, atomic force microscope (AFM), Raman spectrometer, photoluminescence (PL) spectrometer, and high-resolution X-ray diffractometer. It was shown that the newly developed MPCVD reactor can produce diamond films with high quality and purity.

During single-crystal diamond growth by microwave plasma chemical vapor deposition (MPCVD), polycrystalline diamonds are prone to growing at the edge regions. This substantially reduces the usable area of the grown diamond. In recent years, a series of experimental studies have been carried out to solve this, and some achievements have been obtained. However, to understand the diamond growth mechanism more deeply, the relationship between growth quality and various influencing factors still needs to be studied quantitatively through simulations. The plasma density and substrate temperature are important factors that affect the quality of diamond crystallization. In this paper, the growth conditions of the diamond were simulated and compared with the experiments. The results showed that the temperature distribution on the substrate surface was uniform in the axial direction, while the CH₃, H, and electron number density decreased significantly at the edge regions. When the substrate holder mentioned in the literature was used for growth, it was found that the number density uniformity of CH₃, H, and electrons on the substrate surface improved significantly, without changing the temperature uniformity, and so did the edge quality of the grown diamond. However, the average growth rate decreased significantly and, combined with the approximate growth rate formula, it was found that the number density of CH₃ and H on the substrate surface decreased significantly. The main reason for this was that the substrate holder was too high, which led to the substrate reaching the growth temperature at lower deposition conditions. Therefore, a substrate holder with a 6 mm height reduction was designed for simulation and experiment. The edge quality of the grown diamond with this substrate holder was better than that found using the previous substrate holder, and the growth rate was significantly improved. However, there was still a gap in the growth rate compared with results without the substrate holder. Finally, a substrate ring was proposed, to achieve the goal of high quality and high growth rate at the same time.