C. H. Cheng

Use of a High-Work-Function Ni Electrode to Improve the Stress Reliability of Analog

We have studied the stress reliability of low-energy-bandgap high- metal-insulator-metal capacitors under constant voltage stress. By using a high-work-function Ni electrode (5.1 eV), we reduced the degrading effects of stress on the capacitance variation (DeltaC/C), the quadratic voltage coefficient of capacitance (VCC-alpha), and the long-term reliability, in contrast with using a TaN. The improved stress reliability for the Ni electrode capacitors is attributed to a reduction of carrier injection and trapping.

\hbox{SrTiO}_{3}

Using nanocrystal (nc) TiO₂ and TaON buffer layer, the Ni/GeO_x/nc-TiO₂/TaON/TaN resistive random access memory (RRAM) showed forming-free resistive switching, self compliance set/reset currents, excellent current distribution, low 0.7-pJ switching energy, and long 10¹⁰ cycling endurance. The very long endurance in this novel RRAM may create new applications beyond Flash memory.

Metal–Insulator–Metal Capacitors

An investigation of the proton dynamics inside a Nafion membrane has been carried out by molecular dynamics simulations. The atomistic analysis was performed at four different hydration levels (4.21, 8.61, 12.65, and 21.60 wt %) and three operation temperatures (333, 343, and 353 K). The simulation results show a distinct ionic segregation toward the hydrophobic (near fluorocarbon) and hydrophilic (close to the sulfonated acid groups) regions inside the membrane. The number of water clusters at high hydration levels increases significantly compared to the lower cases. A higher temperature tends to magnify the size of the hydrophilic phase; both increase the proton diffusivity. Apart from the effect analysis, this paper also explains the nanoscopic mechanism of the proton transport and further relates it to the molecular structure of the electrolyte membrane.

Long-Endurance Nanocrystal

Using stacked covalent-bond-dielectric GeOx, on metal-oxynitride HfON, the Ni/GeOx/HfON/TaN resistive random access memory (RRAM) showed ultralow set power of 0.3 μW (0.1 μA at 3 V), reset power of 0.6 nW (-0.3 nA at -1.8V), fast 20-ns switching time, ultralow 8-fJ switching energy (4-V overstress), and excellent 106 cycling endurance. Such excellent performance was reached by using hopping conduction with negative temperature coefficient (TC) rather than the positive TC in metal-oxide RRAM.

\hbox{TiO}_{2}

Using stacked covalent-bond-dielectric GeOx, on metal-oxynitride HfON, the Ni/GeOx/HfON/TaN resistive random access memory (RRAM) showed ultralow set power of 0.3 μW (0.1 μA at 3 V), reset power of 0.6 nW (-0.3 nA at -1.8V), fast 20-ns switching time, ultralow 8-fJ switching energy (4-V overstress), and excellent 106 cycling endurance. Such excellent performance was reached by using hopping conduction with negative temperature coefficient (TC) rather than the positive TC in metal-oxide RRAM.

Resistive Memory Using a TaON Buffer Layer

This paper presents the ionic dynamics simulation of an intermediate-temperature solid oxide fuel cell electrolyte. The example electrolyte is a yttria-doped ceria which was proved experimentally to have better performance than the traditional yttria-stabilized zirconia in the intermediate-temperature operation range (below 1073 K). This paper employs the molecular dynamics technique to analyze the oxygen-ion transportation from a nanoscale aspect. The simulation reveals that the oxygen vacancy tends to be constrained near the Y 3+ ions in the crystalline lattice. The influence of different operation temperatures and various Y 2 O 3 concentrations on the ionic conductivity was studied. The results show that 10.1 mol % of Y 2 O 3 doping concentration tends to have the optimal ionic conductivity, while the system temperature tends to increase the ionic conductivity proportionally. The simulation has been compared with published experimental data and shows reasonable agreement in both trend and order of magnitude.

Atomistic Analysis of Hydration and Thermal Effects on Proton Dynamics in the Nafion Membrane

We have fabricated high-K Ni/TiZrO/TaN metal-insulator-metal (MIM) capacitors. A low leakage current of 3.3 x 10 -8 A/cm 2 at -1 V was obtained for a 18 fF/μm 2 capacitance density. For a 5.5 fF/μm 2 capacitance density device, a small voltage coefficient of capacitance a of 105 ppm/V 2 and temperature coefficient of capacitance of 156 ppm/°C were measured.

Ultralow Switching Energy Ni/ /HfON/TaN RRAM

This paper describes the computer simulation of electrochemical flow phenomena to predict the performance of proton exchange membrane fuel cells (PEMFCs), which include hydrogen and direct methanol fuel cells (DMFCs). To study the transport phenomena inside the low temperature fuel cells, the mass, the momentum, and the species equations are required. Darcy laws were employed to simplify the momentum equations in the porous diffusion layers and also to linearize the conservation equation set. That reduces the computational load significantly without losing the generality of the flow field. Performance simulation results were validated with some published experimental data. The comparison shows satisfactory agreement between them. This virtual performance test bench plays an important role in the prototype fuel cell design. The computer aided design tool is able to provide detailed information on the transport phenomena of the fuel cells, in which the flow visualization is not easy to carry out by experiments.

Ultralow Switching Energy Ni/GeO x /HfON/TaN RRAM

In this paper, the impact of Al 2 O 3 incorporation on the electrical characteristics of the SrTiO 3 (STO) metal―insulator―insulator (MIM) capacitor was studied. The Al 2 O 3 -doped STO (STO:Al 2 O 3 = 3:1) MIM provides a high capacitance density ( 14.6 fF/μm 2 ) and a very low leakage current density (9.2 X 10- 9 A/cm 2 at - 1 V) at the same time. The significant enhancement of the conduction band offset and bandgap due to Al 2 O 3 incorporation reduces leakage current largely while maintaining the favorable properties of STO, such as a large high-κ value, a small temperature coefficient of capacitance, and paraelectricity (no fatigue or aging problem) in the operating temperature range of devices. Meanwhile, we also made a comparison among pure STO, Al 2 O 3 -doped STO, and HfO 2 -doped STO MIM capacitors. Results revealed that STO MIM and HfO 2 -doped STO MIM capacitors both show higher capacitance densities, while the leakage current of the Al 2 O 3 -doped STO MIM is much lower than those of both the STO MIM and HfO 2 -doped STO MIM capacitors, which meets the strict requirement of the International Technology Roadmap for Semiconductors 2018. Therefore, the excellent result suggests that the Al 2 O 3 -doped STO film is a potential candidate material for dynamic random access memory and radio-frequency applications.

Ionic Dynamics of an Intermediate-Temperature Yttria-Doped-Ceria Electrolyte

This paper analyzes the transport phenomenon of a solid oxide fuel cell (SOFC) from micro and macro aspects. The micro-scale model focuses on the ion hopping transportation inside the solid electrolyte and the macro-scale model aims at the flow phenomenon and thermal management inside the diffusion layers and the flow channel. In SOFCs, oxygen ions are conducted through the ceramic membrane of Yttria-Stablized Ziconia (YSZ), which is composed of ZrO2 and Y2 O3 . This paper uses molecular dynamics (MD) method to evaluate the ion conductivity of the solid electrolyte. Doping with different percentage of Y2 O3 , the ion hopping simulation shows that about 8 mole % gives the optimal performance. Also the higher the operation temperature, the better the ion conduction. Temperature field management is also a critical issue in the SOFC design. A set of three-dimensional computational fluid dynamics (CFD) model (including mass, momentum, energy and concentration equations) inside the porous diffusion layers and the flow channel of the SOFC were employed to estimate the cooling effect under different pattern of flow channel designs. All simulation results were validated with experiments reported from other literatures. The integration of the micro and macro-scale analyses proves to be versatile in the SOFC prototype design.Copyright