Dr. Ge Chen’ team of Institute of Physics Chinese Academy of Sciences designed a high-performance synaptic transistor based on topotactic phase transformation material (SrFeO2.5？SrFeO3) through the O^2- ion exchange by ionic liquid gating. This work was published in Advanced Materials (Advanced Materials 31, 1900379, 2019). The research team prepared a high-quality SrFeO_2.5 thin film through laser molecular beam epitaxy (Laser-MBE) technique. It was demonstrated that the topotactic modulation of SrFeO_2.5 phase transforms the brownmillerite (BM) SrFeO_2.5 and perovskite (PV) SrFeO_3-δ, through controlling the insertion and extraction of oxygen ions with ionic liquid gating. The phase transformation process is accompanied by changing in the crystal structure, electrical conductivity, and optical absorption characteristics. By the way, the physical properties can be maintained for at least one year after topotactic phase transition. To examine the valence band electronic structures, soft X-ray absorption spectra (XAS) were performed on the 4B9B beamline of the Beijing Synchrotron Radiation Facility (BSRF). This result of XAS experiments confirms that the changes in the Fe valence state and oxygen content occurs via a gating process, reflecting the modified electronic structures. Based on a topotactic phase transition between crystalline phases, we presented a three-terminal ferrite synaptic device. We designed an electrolyte-gated transistor architecture using pristine BM-SFO epitaxial films as the channel material. A synaptic transistor with electrolyte-gated ferrite films by harnessing gate-controllable multilevel conduction states, which is based on controlling the channel conductance via the insertion and extraction of O^2- ions through electrolyte gating. The conductance (≈5 nS) of the SFO-based synaptic transistor is very low, which is particularly important for designing neural networks with large-scale device arrays.

Fig. Electrolyte-gated synaptic transistor based on topotactic phase transformation materials

Article:

Chen Ge,* Chang-xiang Liu, Qing-li Zhou, Qing-hua Zhang, Jian-yu Du, Jian-kun Li, Can Wang, Lin Gu, Guo-zhen Yang, and Kui-juan Jin*. A Ferrite Synaptic Transistor with Topotactic Transformation. Advanced Materials 31, 1900379 (2019).