Shaoan Yan

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 (S < 60 mV/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.

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 (300 nm) as ferroelectric thin film and HfTaO (6 nm, 8 nm, 10 nm, and 12 nm) 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.

Molecular dynamics study of structural damage in amorphous silica induced by swift heavy-ion radiation

ABSTRACT In this paper, the radiation defects induced by the swift heavy ions and the recoil atoms in amorphous SiO2 were studied. The energy of recoil atoms induced by the incident Au ions in SiO2 was calculated by using Monte Carlo method. Results show that the average energies of recoils reach the maximum (200 eV for Si and 130 eV for O, respectively) when the incident energy of Au ion is 100 MeV. Using Tersoff/zbl potential with the newly built parameters, the defects formation processes in SiO2 induced by the recoils were studied by using molecular dynamics method. The displacement threshold energies (Ed) for Si and O atoms are found to be 33.5 and 16.3 eV, respectively. Several types of under- and over-coordinated Si and O defects were analyzed. The results demonstrate that Si3, Si5, and O1 are the mainly defects in SiO2 after radiation. Besides, the size of cylindrical damage region produced by a single recoil atom was calculated. The calculation shows that the depth and the radius are up to 2.0 and 1.4 nm when the energy of recoils is 200 eV. Finally, it is estimated that the Au ion would induce a defected track with a diameter of 4 nm in SiO2.

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.

Influence of the annealing temperature of the Bi4Ti3O12 seeding layer on the structural and electrical properties of Bi3.15Nd0.85Ti2.99Mn0.01O12 thin films

Highly (117)-preferred Bi3.15Nd0.85Ti2.99Mn0.01O12 (BNTM) thin films with a Bi4Ti3O12 (BTO) seeding layer were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by using a sol–gel method. The effects of the Bi4Ti3O12 (BTO) seeding layer under different annealing temperatures ranging from 550 to 700 °C on the structural and electrical properties of BNTM were investigated. X-ray diffraction results indicated that the BNTM thin films with a BTO layer processed with the annealing temperature of 600 °C exhibited the highest (117) orientation at a degree of 97.33%. This typical BNTM film also had the largest remanent polarization (2Pr = 114.5 μC cm−2), dielectric constant (er = 614.9) and dielectric tunability (16.9%) as compared to the BNTM thin films without a seeding layer or with the BTO layer processed at a different temperature. It is also found that the significant enhancement of the piezoelectric properties was achieved in these typical BNTM thin films. Additionally, the BNTM thin films with BTO seeding layers displayed better fatigue properties, degraded by only 1.1% after 109 pulse cycles as compared to 30.2% for those without seeding layers. The mechanism of the temperature dependence of BTO seeding layer on the properties of BNTM will be discussed.

Ionizing radiation effect on metal–ferroelectric–insulator–semiconductor memory capacitors

A theoretical model was developed to investigate the ionizing radiation effect on the electrical characteristics of metal–ferroelectric–insulator–semiconductor (MFIS) structure capacitors under exposure to radiation and under post-irradiation conditions. In this model, the radiation-induced degradation in the ferroelectric layer, oxide layer and silicon dioxide interface were considered, and the radiation effect of the silicon substrate was also taken into account to accommodate the dose rate effect. The modeling results showed that both the capacitance versus applied voltage (C–V) curves and the surface potential versus applied voltage (ΦS(Si)– V) curves shifted significantly and the memory window became worse with increasing total dose. Moreover, the derived results indicated that the symmetry of the polarization versus applied voltage (P–V) curves degraded with the increase in total dose, which may explain the phenomena of radiation-induced fatigue and imprint. These results can provide some insights into the estimation of the radiation-induced degradation of MFIS structure devices and may be integrated into electronic design automation (EDA) software for ionizing radiation effect simulation.

A novel methodology of layout design by applying euler path

A new methodology of layout design applying Euler path is proposed. By separating the pFET array and nFET array away, and then mapping them to be diffusion graphs, we can reduce the operational complexity when solving Euler path and generating the stacked layout. The means that making use of adjacency matrix of diffusion graph to identify Euler path and adding dummy edge in advance could make Atallah algorithm simplified. In addition, some optimization to the Atallah algorithm is also investigated.

Polarization switching and fatigue characteristics of highly (117)-oriented Bi3.15Nd0.85Ti2.99Mn0.01O12 ferroelectric thin films at both low and elevated temperatures

Polarization switching and fatigue properties of highly (117)-oriented Bi3.15Nd0.85Ti2.99Mn0.01O12 (BNTM) ferroelectric thin films were studied at both low and elevated temperatures (100 K up to 475 K). The fatigue behavior of BNTM thin films displays little dependence on temperature below 200 K, which can be explained by a weak domain wall pinning and unpinning effect. In the temperature range of 200 and 300 K, the polarization fatigue of BNTM films becomes exacerbated, which can be ascribed to a stronger domain pinning effect and increased electron injection from the Schottky barrier at film/electrode interfaces. However, the films showed improved fatigue endurance as the temperature increases from 300 to 400 K. From the temperature-dependent impedance spectra analysis we have learned that the long-range diffusion of oxygen vacancies within their clusters and strong domain unpinning effect may be responsible for this trend. Using the in-plane PFM phase image, observations of the microscopic evolution of domains and charged domain walls were made, and charged domain walls caused by head-to-head or tail-to-tail polarization configurations were found. Thus a combination of impedance spectra techniques and PFM domain observations can be a powerful technique, and has been used in this study to analyze the mechanisms of polarization fatigue at both low and elevated temperatures for the layered perovskite structure BNTM thin films.

3-D simulation of charge collection in double-gate MOSFET under low-energy proton irradiation

The charge collection in 20 nm double-gate MOSFET (DG MOSFET) submitted to low-energy Proton irradiation are investigated in this paper. The drain current transient and charge collection with different doping levels are simulated. Different strike radii and locations are also discussed in the paper.

Radiation hardened by design techniques to mitigating P-hit single event transient

As technologies scale down in size, the single event effect has become a universal phenomenon. In this work, a new radiation hardened by design (RHBD) technique has been proposed to mitigating P-hit single event transient. This method is named here as the 3 transistor common drain (3TCD) method. With simulations of the inverter chain using a three-dimensional (3D) technology computer-aided design (TCAD) simulation tool, it has been found that this new 3TCD method has an obvious effect on the p-channel metal-oxide semiconductor field-effect transistor (PMOS FET) by mitigating single event transient (SET) pulse widths (WSET).