29.8 SHARC: Self-Healing Analog with RRAM and CNFETs

Carbon nanotube (CNT) field-effect transistors (CNFETs) are a promising emerging technology for energy-efficient electronics (Fig. 29.8.1). Despite this promise, CNTs are subject to substantial inherent imperfections; every ensemble of CNTs includes some percentage of metallic CNTs (m-CNTs). m-CNTs result in conductive shorts between CNFET source and drain, resulting in excessive leakage and degraded (potentially incorrect) circuit functionality (Fig. 29.8.1). Several techniques have been developed to remove the majority of m-CNTs (no technique today removes 100% of m-CNTs). While these techniques enabled the first digital CNFET circuits, it is still not possible to realize large-scale CNFET analog or mixed-signal CNFET circuits due to m-CNTs. As shown in Fig. 29.8.1, while a digital logic gate can still function correctly in the presence of a small fraction of m-CNTs (but with degraded resilience to noise) [1], a single m-CNT in an analog circuit can result in catastrophic failure (e.g., degrading amplifier gain resulting in functional failure of circuit blocks such as ADCs and DACs)
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. This paper presents a circuit design technique, Self-Healing Analog with RRAM and CNFETs (SHARC), that leverages the programmability of non-volatile resistive RAM (RRAM) to automatically “self-heal” analog circuits in the presence of m-CNTs. Using SHARC, we experimentally demonstrate analog CNFET circuits robust to m-CNTs as well as the first mixed-signals CNFET sub-system (4-bit DAC and SAR ADC; these are the largest reported complementary (CMOS) CNFET circuit demonstrations to-date).