CMOS Reliability Characterization Techniques and Spintronics-Based Mixed-Signal Circuits

Abstract

Plasma-Induced Damage (PID) has been an important reliability concern for equipment vendors and fabs in both traditional SiO2 based and advanced high-k dielectric based processes. Plasma etching and ashing are extensively used in a typical CMOS back-end process. During the plasma steps, the metal interconnect, commonly referred to as an “antenna,” collects plasma charges and if the junction of the driver is too small to quickly discharge the node voltage, extra traps are generated in the gate dielectric of the receiver thereby worsening device reliability mechanisms such as Bias Temperature Instability (BTI) and Time Dependent Dielectric Breakdown (TDDB). The foremost challenge to an effective PID mitigation strategy is in the collection of massive TDDB or NBTI data within a short test time. In this dissertation, we have developed two array-based on-chip monitoring circuits for characterizing latent PID including (1) an array-based PID-induced TDDB characterization circuit and (2) a PID-induced BTI characterization circuit using the 65nm CMOS process. As the research interest on analog circuit reliability is increasing recently, a few studies analyzed the impact of short-term Vth shift, not a permanent Vth shift, on a Successive Approximation Register (SAR) Analog-to-Digital Converter (ADC) and revealed that even short-term Vth shifts in the order of 1mV by short stress pulse (e.g., 1μs) on the comparator input transistors may cause to degrade the resolution of the SAR ADC even for a fresh chip (no experimentally verified). In this dissertation, we quantified this effect through test-chip studies and propose two simple circuit approaches that can be used to mitigate short-term Vth instability issues in SAR ADCs. The proposed techniques were implemented in 10-bit SAR ADC using the 65nm CMOS process. Spintronic circuits and systems have several unique properties including inherent non-volatility that can be uniquely exploited for achievable functional capabilities not obtainable in conventional systems. Magnetic Tunnel Junction (MTJ) technology has matured to the point where commercial spin transfer torque MRAM (STT-MRAM) chips are currently being developed. This work aims at leveraging and complimenting on-going development efforts in MTJ technology for non-memory mixed-signal applications. In this dissertation, we developed two spintronics-based mixed-signal circuit designs: (1) an MTJ-based True Random Number Generator (TRNG) and (2) an MTJ-based ADC. The proposed TRNG and ADC have the potential to achieve a compact area, simpler design, and reliable operation as compared to their CMOS counterparts.