Flexible unified memory for multi-functioning nonvolatile memory and ultrafast 1T-DRAM

Abstract

Flexible electronics have attracted great attention as one of the promising future technologies, advantageous over traditional inorganic semiconductor devices on rigid substrates due to their widespread applications enabled by the mechanical bendability. Accordingly, flexible memories have been developed to realize the fully functional flexible systems with data storage ability and for the advanced system with circuital implementation. However, most of the flexible electronics and memory devices reported to date are in large feature size with relatively poor performance compared to the conventional silicon wafer-based CMOS devices and memories. The main crucial reasons arise from the definite limitations of the nature of the flexible substrates, that plastics have low thermal stability and susceptibility to chemicals. Therefore there are material limitations available on plastics, and sophisticated fabrication processes used for conventional CMOS fabrication are unavailable on plastics, resulting low performance with large feature size. Here, we show for the first time flexible high-performance inorganic memory transistors that perform excellent memory properties with highly scaled down dimension as similar as the traditional wafer-based rigid memory devices. This achievement is realized through the introduction of the wafer thinning technique cooperating with the transfer printing process. By wafer thinning, the memory transistors made by conventional CMOS fabrication are transformed in the flexible form. The trilayer dielectric structure was implemented for charge trapping during nonvolatile memory functions, and the FinFET structure was adopted to accommo-date the floating body effect required for the 1-T DRAM operation. The flexible nonvolatile memory characteristics presented here shows the best performance of the flexible memories in our knowledge, even satisfying the traditional technical specifications of the commercialized nonvolatile memories. In addition, flexible ultrafast 1 transistor dynamic random access memory (1T-DRAM) operation is demonstrated for the first time. Furthermore, the flexible memory transistors reported here demonstrates ‘unified memory’ characteristics that function as both the nonvolatile memory and the ultrafast DRAM in a single transistor device. Stable flexibility is confirmed that the memory transistors are not damaged withstanding the mechanical bending and the bending cycles. These results are believed to be a significant approach to the fully integrated high-density flexible systems with the processor-level functionality.