Graphene Field-Effect Transistors with Ferroelectric Gating

Recent experiments on ferroelectric gating have introduced a novel functionality, i.e., nonvolatility, in graphene field-effect transistors. A comprehensive understanding in the nonlinear, hysteretic ferroelectric gating and an effective way to control it are still absent. In this Letter, we quantitatively characterize the hysteretic ferroelectric gating using the reference of an independent background doping ($n_{\mathrm{BG}}$) provided by normal dielectric gating. More importantly, we prove that $n_{\mathrm{BG}}$ can be used to control the ferroelectric gating by unidirectionally shifting the hysteretic ferroelectric doping in graphene. Utilizing this electrostatic effect, we demonstrate symmetrical bit writing in graphene-ferroelectric field-effect transistors with resistance change over 500% and reproducible no-volatile switching over ${10}^5$ cycles.

Figure 1

(a) Sample geometry of GFeFETs. (b) $R$ vs $V_{\mathrm{BG}}$ of one sample after PVDF coating. The red open square and black solid line are the experimental and fitting results, respectively. Inset: Atomic force microscopy of the sample after PVDF. Color scale: 0–164 nm.

Figure 2

(a) $R$ vs $V_{\mathrm{TG}}$ and $V_{\mathrm{BG}}$ of the GFeFET with very small $|P_r|$. (b) Extracted single traces of $R$ vs $V_{\mathrm{TG}}$ with different $V_{\mathrm{BG}}$. The blue dotted lines are simulated results. (c) $n_{\mathrm{BG}}$ tunable doping hysteresis in GFeFETs. Only three doping hysteresis loops, corresponding to experimental curves (i), (ii), and (iii) in Fig. 2b, are shown for clarity. See the main text for discussions.

Figure 3

(a) $\Delta R/R$ as a function of $V_{\mathrm{BG}}$ with different $V_{\mathrm{TG}\max }$. Two maxima are observable with $V_{\mathrm{TG}\max }=5\mathrm{V}$ (black open circles). The red solid line shows the simulation with $\beta P_r=4.2\times {10}^{11}{\mathrm{cm}}^{-2}$. For $V_{\mathrm{TG}\max }=30\mathrm{V}$, the maximum $△R/R$ is increased to 500% ($V_{\mathrm{BG}}=32\mathrm{V}$). (b) $R$ ($V_{\mathrm{TG}}$, $V_{\mathrm{BG}}$) of the GFeFET with higher $\beta P_r$ ($\sim 2\times {10}^{12}{\mathrm{cm}}^{-2}$). Double peak structures dominate over the whole $V_{\mathrm{BG}}$ range.

Figure 4

Symmetrical bit writing in GFeFETs with $n_{\mathrm{BG}}\approx -\beta P_r/e$. (a),(b) Writing 1 by using $-V_{\mathrm{writing}}$. (c),(d) Writing 0 by using $V_{\mathrm{writing}}$. Dashed and solid arrows indicate the forward and backward voltage sweep directions, respectively. The writing is independent on the initial states. (e),(f) Fatigue test of one GFeFET with symmetrical bit writing, showing nonvolatile switching cycles exceeding 100 k.