Y. G. Xiao

Surface-Potential-Based Drain Current Model for Long-Channel Junctionless Double-Gate MOSFETs

A surface-potential-based model is developed for the symmetric long-channel junctionless double-gate MOSFET. The relationships between surface potential and gate voltage are derived from some effective approximations to Poissons equation for deep depletion, partial depletion, and accumulation conditions. Then, the Pao-Sah integral is carried out to obtain the drain current. It is shown that the model is in good agreement with numerical simulations from subthreshold to saturation region. Finally, we discuss the strengths and limitations (i.e., threshold voltage shifts) of the JLFET, which has been recently proposed as a promising candidate for the JFET.

Bipolar and unipolar resistive switching behaviors of sol–gel-derived SrTiO3 thin films with different compliance currents

The SrTiO3 (STO) thin fi lms on aP t/Ti/SiO2/Si substrate were synthesized using a sol–gel method to form a metal–insulator–metal structure. This device shows the bipolar resistance switching (BRS) behavior for a compliance current Icc of less than 0.1 mA but exhibits soft breakdown at a higher level of compliance current. A transition from the BRS behavior to the stable unipolar resistive switching behavior (URS) was also observed. We found that the BRS behavior may be controlled by the structure interface while the URS behavior is likely bulk controlled. Our study indicates that the external compliance current is a key factor in resistance switching phenomenon of STO thin films. (Some figures in this article are in colour only in the electronic version)

Bipolar and unipolar resistive switching modes in Pt/Zn0.99Zr0.01O/Pt structure for multi-bit resistance random access memory

In this work, we report the coexistence of bipolar resistive switching (BRS) and unipolar resistive switching (URS) modes in Pt/Zn0.99Zr0.01O/Pt structure device. After the forming process, this device with URS behavior exhibits either URS mode in the same direction or BRS mode in the opposite direction during the reset process. Controllable multi-state resistances in the low and high resistance states for the BRS mode were obtained by imposing different compliance currents (Icc) and the span of voltage sweeping in the reset process (Vstop). These results suggest that our devices have high potential for the next generation of nonvolatile memory applications.

Simulation of electrical characteristics in negative capacitance surrounding-gate ferroelectric field-effect transistors

The electrical characteristics of surrounding-gate (SG) metal-ferroelectric-semiconductor (MFS) field-effect transistors (FETs) were theoretically investigated by considering the ferroelectric negative capacitance (NC) effect. The derived results demonstrated that the NC-SG-MFS-FET displays superior electrical properties compared with that of the traditional SG-MIS-FET, in terms of better electrostatic control of the gate electrode over the channel, smaller subthreshold swing (Su2009<u200960u2009mV/dec), and bigger value of ION. It is expected that this investigation may provide some insight into the design and performance improvement for the fast switching and low power dissipation applications of ferroelectric FETs.

Temperature effect on electrical characteristics of negative capacitance ferroelectric field-effect transistors

The electrical properties of negative capacitance (NC) ferroelectric field-effect transistors (FeFETs) were theoretically investigated in the temperature range from 280 to 360u2009K. The derived results indicate that for a fixed thickness of ferroelectric thin film the amplification of surface potential can be tuned by temperature. The transfer and output characteristics degrade with increasing temperature due to the gradual loss of ferroelectric NC effect. It is expected that the derived results may provide some insight into the design and performance improvement for the low power dissipation applications of FeFETs.

Enhanced ferroelectric, dielectric and leakage properties in Ce and Ti co-doping BiFeO3 thin films

Pure BiFeO3 (BFO), Ce and Ti individual doping and co-doping BiFeO3 thin films were fabricated via sol–gel process on Pt/Ti/SiO2/Si substrates. The microstructure, surface morphology, ferroelectric and dielectric properties of BFO and doped thin films were investigated in detail. X-ray diffraction reveal that all thin films are confirmed the formation of the distorted rhombohedral perovskite structure. No impure phase is identified in all the films. The Ce and Ti co-doping BiFeO3 (BCFTO) thin films exhibited the enhanced ferroelectricity with a large remnant polarization (2Pr) of 130xa0μC/cm2, and low leakage current density of 9.10xa0×xa010−6xa0A/cm2 which is more than two orders of magnitude lower than that of pure BFO films at 100xa0kV/cm. The dielectric constant (364 at 1xa0kHz) of the BCFTO thin films is much larger than that of pure BFO thin films. These results suggest that the introductions of Ce and Ti provides an effective route for improving the ferroelectric, dielectric and leakage properties of BFO thin films.

Impact of total ionizing dose irradiation on Pt/SrBi2Ta2O9/HfTaO/Si memory capacitors

In this work, metal-ferroelectric-insulator-semiconductor (MFIS) structure capacitors with SrBi2Ta2O9 (300u2009nm) as ferroelectric thin film and HfTaO (6u2009nm, 8u2009nm, 10u2009nm, and 12u2009nm) as insulating buffer layer were proposed and investigated. The prepared capacitors were fabricated and characterized before radiation and then subjected to 60Co gamma irradiation in steps of two dose levels. Significant irradiation-induced degradation of the electrical characteristics was observed. The radiation experimental results indicated that stability and reliability of as-fabricated MFIS capacitors for nonvolatile memory applications could become uncontrollable under strong irradiation dose and/or long irradiation time.

Large memory window and good retention characteristics of ferroelectric-gate field-effect transistor with Pt/Bi3.4Ce0.6Ti3O12/CeO2/Si structure

Bi4?xCexTi3 O12(x?=?0.0, 0.4, 0.6 and 1.0) ferroelectric-thin films were fabricated by chemical solution deposition. Among these thin film samples, Bi3.4Ce0.6Ti3O12 (BCT) exhibits the best ferroelectric property. An n-channel metal?ferroelectric?insulator?silicon (MFIS) ferroelectric-gate field-effect transistor (FeFET) with Pt/BCT/CeO2/Si structure was fabricated and characterized. Due to the relatively good interface properties between the insulator layer (CeO2) and ferroelectric-gate layer (BCT), the device shows a nearly unchanged memory window of about 3.2?V after a 24?h retention test and a field-effect mobility of approximately 24.6?cm2?V?1?s?1. These results suggest that the Pt/BCT/CeO2/Si FeFET is suitable for high-performance ferroelectric memory application.

An improved model for the surface potential and drain current in negative capacitance field effect transistors

An improved model for the surface potential and drain current in negative capacitance ferroelectric field effect transistors (NC-FeFETs) was presented by introducing the doping concentration. The influence of the doping concentration and temperature on the electric characteristics of NC-FeFET was investigated based on this model. The derived results demonstrated that the subthreshold slope of the metal–ferroelectric–semiconductor NC-FeFET increases, while the drive current decreases when the substrate doping concentration increases from 1017 m−3 to 1020 m−3. Additionally, in the temperature range from 290 K to 380 K, the voltage amplification gradually shrinks, resulting in the subthreshold swing increasing from 51 mV dec−1 to 71 mV dec−1. These results indicated that silicon doping concentration and temperature are two key factors for optimizing the operation voltage in NC-FeFETs.

Microstructure, Phase Transition, and Piezoelectric Properties of Cerium-Substituted Bismuth Titanate Nanofibers

Cerium-substituted bismuth titanate (BCT) nanofibers were synthesized using sol–gel-based electrospinning. The morphology, crystallized phase, and crystal structure of the nanofibers were characterized by scanning electron microscopy, x-ray diffraction, and transmission electron microscopy, respectively. Fine-crystallinity nanofibers with diameters in the range of 100xa0nm to 200xa0nm and length over 100xa0μm after annealing at 750°C for 1xa0h were obtained. The phase transition of the BCT nanofibers was investigated by thermal analysis, and the Curie temperature was found to be 540°C. A displacement–voltage “butterfly” curve with displacement maximum of 1.1xa0nm was observed by piezoresponse force microscopy, and the maximum value of the piezoelectric coefficient was up to 158xa0pm/V, being attributed to successful Ce co-substitution for both A- and B-sites based on Raman spectrum analysis.