High-performance, rich functions, and low power consumptions are the key trends for advanced intelligent mobile devices. Thus, three dimensional (3D) integrated circuits (IC) with multiple processors (i.e. CPU, GPU, APU), analog circuits, volatile memory (i.e. SRAM and DRAM), and nonvolatile memories (NVM) with (1) high bandwidth (2) low power consumption for vertical signal communications, and (3) cost-effective manufacturing are required for mobile devices. TSV technologies pROVide higher density and less parasitic load compared to conventional wire-bonding approaches. However, TSV brings large dimension and long connect distance, as well as significant parasitic capacitance compared to typical via/contact in CMOS process. Thus, TSV technology can only pROVide limited number of vertical data path and bandwidth.
Recently, 3D sequential integration (3DSI) approaches were proposed to achieve higher density in vertical interconnects than TSV technologies. In 3DSI chips, the thermal impact of the device fabrication must be negligible to avoid the degradation of pre-existing devices, resembling the back-end process. National Nano Device Laboratories(NDL), National Applied Research Laboratories (NARLabs), demonstrated Monolithic 3D Chip Integration technology to stack multiple layers on one chip for the applications of multi-functional super-chips. In this program, high-performance backend UTB MOSFETs in such emerging 3D circuits were developed and deployed in each layer in monolithic 3D circuits by inventing low temperature (LT) ultra-flat and ultrathin Si, a LT pseudo-substrate, super-CMP-planarized laser-crystallized epi-like Si.
This Monolithic 3D circuit technology can enable numerous layers of chips to fit in space once used to stack a mere two chips using traditional TSV 3D circuit technology, and helps impROVe power consumption of signal propagation, and offers new design possibilities. Therefore, such an advanced 3D processed architecture with closely spaced ILD enables high-speed NVMs/logic and SRAM for compact and power-saving mobile products
