Metal Based Nonvolatile Field‐Effect Transistors

Abstract

wileyonlinelibrary.comone or several kinds of molten salt electrolysis, such as CaCl 2 and KCl, to dissolve oxygen. [11][12][13][14][15] Obviously, this electrochemical process cannot be exploited for FET applications because of the involvement of high temperatures and molten salts in the reduction process.In this work, we demonstrate that in a FET structure the transition between metallic Co and insulating CoO x can be achieved at a moderate temperature without the involvement of molten salts. The on and off states of the device can be attained by the M-MO x transition (MMOT), which is controlled by a weak applied electric fi eld at 200 °C and exhibits reversible and nonvolatile behaviors. Contrary to molten salts used in previous MMOT process, [11][12][13][14][15] a rare-earth sesquioxide, Gd 2 O 3 , is used for ion transport. The resistance between source and drain terminals ( R ) can be modulated by a factor of 10 5 , which is comparable to that of other nonvolatile FETs based on graphene or organic materials. [2][3][4][5][6] Furthermore, a clear threshold resistance switching (TRS) behavior is observed at high resistance states, but with an opposite switching direction compared to that observed in usual M/Oxide/M (MOM) structures. [16][17][18][19][20] Results and DiscussionThe central part of FET structures used in this work is a single 4 nm Co layer with the lateral size of 20 × 30 µm 2 , which was patterned from a sputtered Co layer on the top of Si/ SiO2 substrates by standard photolithography and ion etching processes. As shown in Figure 1 , four 10 nm Pt electrodes, a 120 nm Gd 2 O 3 insulating layer, and a Pt 20/Ru 50 (nm) top-gate electrode were also sequentially deposited and patterned. The resistance of as-deposited sample is about 380 Ω, corresponding to the resistivity of 1.01 × 10 −6 Ω m, which is about two orders larger than its bulk value (6.64 × 10 −8 Ω m). We fi rst investigated annealing effects on the resistance. As shown in Figure S1a (Supporting Information), the resistance increased about 55 Ω only after the fi rst annealing process at 220 °C and then maintained nearly the same value under further annealing. Then, if we applied a positive gate voltage (+ V G ) during the subsequent annealing process, the resistance gradually decreased with increasing annealing time, and it dropped even to a smaller value than that of the as-deposited sample (see Supporting Information, Figure S1b). These results verify the role of V G , instead of annealing effects, on the resistance change under following V G operations. Figure 2 a-c shows the current-voltage ( I -V ) characteristic curves measured at room temperature (RT) after applying V G at The reduction of metals from their oxides through solid electrochemical reactions usually requires a high temperature above 800 °C and a specially designed electrochemical structure. It is demonstrated that, in a simple fi eldeffect transistor (FET) structure, the redox reaction between Co metal and CoO x is reversible under a small electric fi eld and can be ac...

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