Excellent low-voltage operating flexible ferroelectric organic transistor nonvolatile memory with a sandwiching ultrathin ferroelectric film

Abstract

The high operating voltage is a primary issue preventing the commercial application of the ferroelectric organic field-effect transistor (Fe-OFET) nonvolatile memory (NVM). In this work, we propose a novel route to resolve this issue by employing two ultrathin AlO_X interfacial layers sandwiching an ultrathin ferroelectric polymer film with a low coercive field, in the fabricated flexible Fe-OFET NVM. The operation voltage of Fe-OFET NVMs decreases with the downscaling thickness of the ferroelectric film. By inserting two ultrathin AlO_X interfacial layers at both sides of the ultrathin ferroelectric film, not only the gate leakage is prominently depressed but also the mobility is greatly improved. Excellent memory performances, with large mobility of 1.7 ~ 3.3 cm² V^-1 s^-1, high reliable memory switching endurance over 2700 cycles, high stable data storage retention capability over 8 × 10⁴ s with memory on-off ratio larger than 10², are achieved at the low operating voltage of 4 V, which is the lowest value reported to data for all Fe-OFET NVMs. Simultaneously, outstanding mechanical fatigue property with the memory performances maintaining well over 7500 bending cycles at a bending radius of 5.5 mm is also achieved in our flexible FE-OFET NVM.

Figure 1

(a) Photograph and (b) schematic configuration of the flexible Fe-OFET NVM. AFM images of (c) 60 nm thick P(VDF-TrFE-CTFE) film (2 μm × 2 μm), (d) AlO_X interfacial layer (2 μm × 2 μm) and (e) pentacene film (5 μm × 5 μm).

Figure 2

Transfer characteristics of the Fe-OFET NVMs with a downscaling P(VDF-TrFE-CTFE) film at different thicknesses of (a) 205, (b) 150, (c) 100, (d) 60 and (e) 40 nm, respectively, operating at different V _G sweeping ranges. (f) Dependence of the saturated ΔV _T and the corresponding electric field (E _F-sat) on the thickness of P(VDF-TrFE-CTFE) films.

Figure 3

The leakage current density versus voltage of the capacitors with/without ultrathin AlO_X layers at each side of the 60 nm thick P(VDF-TrFE-CTFE) film.

Figure 4

(a) Memory switching endurance and (b) data storage retention characteristics of the low-voltage operating flexible Fe-OFET NVM with a 60 nm thick P(VDF-TrFE-CTFE) ferroelectric film. (c) Transfer characteristics of the low-voltage operating flexible Fe-OFET NVM measured at the planar and bending states, respectively. (d) Mechanical fatigue property of the low-voltage operating flexible Fe-OFET NVM measured at a bending radius of 5.5 mm.