A Ge-Channel Ferroelectric Field Effect Transistor With Logic-Compatible Write Voltage

• Published in: IEEE electron device letters Vol. 44; no. 2; pp. 257 - 260
• Main Authors: Das, Dipjyoti, Ravindran, Prasanna Venkatesan, Park, Chinsung, Tasneem, Nujhat, Wang, Zheng, Chen, Hang, Chern, Winston, Yu, Shimeng, Datta, Suman, Khan, Asif
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.02.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Delays; Dielectric constant; Electric potential; endurance; FeFETs; FEOL; Ferroelectric materials; Ferroelectricity; Field effect transistors; Ge-channel; Germanium; Germanium oxides; memory window; Permittivity; Pulse measurements; read-after-write; Reduction; retention; Semiconductor devices; Silicon dioxide; Voltage; Voltage measurement; write voltage
• ISSN: 0741-3106; 1558-0563
• DOI: 10.1109/LED.2022.3231123

A major roadblock for the integration of ferroelectric-field-effect transistors (FEFETs) at advanced technology nodes for embedded memory applications is their high, logic-incompatible write voltages. Herein, we explore Ge as a channel material to reduce write voltage of FEFET and report the first demonstration of p-type Ge-FEFETs with record low write voltages of ±1.4 V with a memory window (MW) of 0.6 V at DC and write voltages of ±1.4 V, ±1.8 V and ±2.4 V for MW of 0.2 V, 0.5 V and 0.8 V for a write time of 10 <inline-formula> <tex-math notation="LaTeX">\mu \text{s} </tex-math></inline-formula>, respectively. The write voltages observed in Ge-pFEFETs are ~50% lower than that of a Si-pFEFETs when compared against iso-memory window condition [±2.5 V with a MW of 0.6 V at DC, ±3.5 V for MW of 0.5 V for a write time of 10 <inline-formula> <tex-math notation="LaTeX">\mu \text{s} </tex-math></inline-formula>]. Such dramatic reduction of write voltages in Ge-pFEFETs is achieved due to the fact that the native oxide of Ge (GeOx), formed at the Ge interface, has a larger dielectric constant and lower thickness than those for SiO2 on the Si platform. In addition, the lower bandgap and higher dielectric constant of Ge may lead to a lower surface potential for a given semiconductor charge, leading to further reduction in the write voltage. Further, our Ge-pFEFETs show write endurance of 107 cycles (the best-in-class for Ge-pFEFETs, as reported in the literature), excellent data retention, and immediate read-after-write capability. Our results indicate the attractiveness of Ge platform for FEFETs for embedded memory applications.