GaN Nanowire-based Ferroelectric Field Effect Transistor And Its Electric Properties

Ferroelectric random access memory(FRAM) is considered as one of the most potential next generation memory because of many advantages such as nonvolatile, low power consumption, high speed, high density, high endurance and irradiation hardness. As one type of FRAM, ferroelectric field effect transistor(Fe FET) has attracted considerable interests due to its characteristics of simple unit structure, nondestructive read-out, higher storage density, and compatible with the process of integrated circuit(IC). However, there is a great number of problems need to be solved in the progress of the nanowire-based Fe FET research. The first key problem eager to be solved is the microtechnic technology to fabricate and investigate the properties of Fe FET. In this thesis, Fe FETs using individual Ga N nanowire as the conducting channel and PZT thin film as the gate dielectric were fabricated innovative with the combination of the lithography and focused ion beam(FIB), and the Fe FETs showed excellent properties. The main research contents and conclusions are as following:1. High quality Ga N nanowires were synthesized using a chemical vapor deposition(CVD) growth process with Au nanoparticles as catalyst, which could be used for the conducting channel of Fe FET. They were suggested to grow by the vapor-liquid-solid(VLS) mechanism. X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and transmission electron microscopy(TEM) were used to characterize the nanowires. The results indicated that the nanowires were straight and the surfaces were relatively smooth. Their lengths were in the range of several tens to several hundreds of micrometers and diameters were in the range of 100-200 nm. The Ga N nanowires had a single-crystalline wurtzite structure and were grew along the [100] direction.2. The PZT thin films were deposited on Pt/Ti/Si O2/Si substrates by RF magnetron sputtering. The films were characterized by XRD, SEM, EDS, Raman scattering spectroscopy and ferroelectric analyzer. The results indicated that a continuous surface smooth and dense without large pinholes and obvious cracks were obtained, and the average grain size of the film ranging from 2 μm to 5 μm. The thickness of the film was about 500 nm. The PZT thin film was of single perovskite structure consists of rhombohedral phase and tetragonal phase. The films had a polarization hysteresis loop under low sweep voltage showed that the polarizing characteristics were excellent.3. Fe FETs using individual Ga N nanowire as the conducting channel and PZT/Pt/Ti/Si O2/Si structure as the back gate were fabricated successful with the combination of the lithography and FIB. The output and transfer characteristics of the individual Ga N nanowire-based Fe FET indicated that the Ga N nanowire channel was of n-type. And the Fe FET showed excellent memory and electrical properties. The memory window was up to 5 V and the on/off current ratio was up to 103 at zero gate voltage. The NW Fe FET exhibited a sub-threshold swing of S = 0.93 V/decade. Its peak transconductance gm was estimated to be gm ≈ 1.7 μS and the field effect electron mobility(μ) in the Ga N nanowire channel was estimated to be 16.4 cm2/V·s.4. The temperature and irradiation dependence of the electrical properties of Pt/SBT/Hf Ta O/Si capacitor was investigated. The results could provide useful guidelines for the research of the temperature and irradiation dependence of the electrical properties of the Fe FETs using individual Ga N nanowire as the conducting channel. This may be helpful for the potential application of FRAM in the cutting-edge technology.The Fe FET employing semiconductor nanowire as conducting channel has excellent properties such as operating at ultra-low power and enhancing operation speed. The results of this thesis could provide useful guidelines for the potential application of nanowires in nonvolatile memory.