Tailoring the number of lines for IGO-channel 2T0C DRAM comparable to conventional 2-line operation 1T1C structure for highly scaled cell volume

Abstract

Capacitor-less 2T0C dynamic random-access memory (DRAM) employing oxide semiconductors (OSs) as a channel has great potential in the development of highly scaled three dimensional (3D)-structured devices. However, the use of OS and such device structures presents certain challenges, including the trade-off relationship between the field-effect mobility and stability of OSs. Conventional 4-line-based operation of the 2T0C enlarges the entire cell volume and complicates the peripheral circuit. Herein, we proposed an IGO (In-Ga-O) channel 2-line-based 2T0C cell design and operating sequences comparable to those of the conventional Si-channel 1 T1C DRAM. IGO was adopted to achieve high thermal stability above 800 degrees C, and the process conditions were optimized to simultaneously obtain a high mu FE of 90.7 cm2<middle dot>V-1<middle dot>s-1, positive Vth of 0.34 V, superior reliability, and uniformity. The proposed 2-line-based 2T0C DRAM cell successfully exhibited multi-bit operation, with the stored voltage varying from 0 V to 1 V at 0.1 V intervals. Furthermore, for stored voltage intervals of 0.1 V and 0.5 V, the refresh time was 10 s and 1 000 s in multi-bit operation; these values were more than 150 and 15 000 times longer than those of the conventional Si channel 1T1C DRAM, respectively. A monolithic stacked 2-line-based 2T0C DRAM was fabricated, and a multi-bit operation was confirmed. The fabrication of IGO channel for DRAM was optimized.Superior electrical reliability and excellent uniformity were achieved.2-line-based 2T0C DRAM cell afforded multi-bit operation and non-volatile memory.Memory properties were improved by decreasing the number of lines.Monolithic stacked 2T0C DRAM required further structural improvement.