Recent Advances in Hollow Cathode Technology for Plasma-Enhanced ALD—Plasma Surface Modifications for Aluminum and Stainless-Steel Cathodes

Recent designs have allowed hollow cathode gas plasma sources to be adopted for use in plasma-enhanced atomic layer deposition with the benefit of lower oxygen contamination for non-oxide films (a brief review of this is provided). From a design perspective, the cathode metal is of particular interest since—for a given set of conditions—the metal work function should determine the density of electron emission that drives the hollow cathode effect. However, we found that relatively rapid surface modification of the metal cathodes in the first hour or more of operation has a stronger influence. Langmuir probe measurements and hollow cathode electrical characteristics were used to study nitrogen and oxygen plasma surface modification of aluminum and stainless-steel hollow cathodes. It was found that the nitridation and oxidation of these metal cathodes resulted in higher plasma densities, in some cases by more than an order of magnitude, and a wider range of pressure operation. Moreover, it was initially thought that the use of aluminum cathodes would not be practical for gas plasma applications, as aluminum is extremely soft and susceptible to sputtering; however, it was found that oxide and nitride modification of the surface could protect the cathodes from such problems, possibly making them viable.

Two-terminal vertical thyristor using Schottky contact emitter to improve thermal instability

In a two-terminal-electrode vertical thyristor, the latch-up and latch-down voltages are decreased when the memory operation temperature of the memory cells increases, resulting in a severe reliability issue (i.e., thermal instability). This study fundamentally solves the thermal instability of a vertical-thyristor by achieving a cross-point memory-cell array using a vertical-thyristor with a structure of vertical n++-emitter, p+-base, n+-base, and p++-emitter. The vertical-thyristor using a Schottky contact metal emitter instead of an n++-Si emitter significantly improves the thermal stability between 293 and 373 K. Particularly, the improvement degree of the thermal stability is increased significantly with the use of the Schottky contact metal work function. Because the thermal instability (i.e., degree of latch-up voltage decrement vs. memory operation temperature) decreases with an increase in the Schottky contact metal work function, the dependency of the forward current density between the Schottky contact metal and p+-Si based on the memory operation temperature reduces with increase in the Schottky contact metal work function. Consequently, a higher Schottky contact metal work function produces a higher degree of improvement in the thermal stability, i.e., W (4.50 eV), Ti (4.33 eV), Ta (4.25 eV), and Al (4.12 eV). Further research on the fabrication process of a Schottky contact metal emitter vertical-thyristor is essential for the fabrication of a 3-D cross-point memory-cell.

Effect of Gate Metal Work-function on Junctionless (JL) Nanowire GAA MOSFET Performance

Metal gate technology is one of the promising methods used to increase the drain current by increasing the electrostatic controllability. Different metals have different work-function that controls the device performance very closely as gate to source voltage is the basic inputs for these. In this paper the dependency of gate metal work-function on device performance (both for nMOS and pMOS) is extensively investigated. The gate metal work-function value is taken as 4.2eV to 5.1eV with one increment to see the change in potential profile. With this condition, the IOn current, IOff current, threshold voltage, transconductance also calculated for these structures. A decrease value in drain current (1e-6 to 1e-7 A) is observed for both the cases with increase in work-function of gate metal. However, the Off current is getting better (1e-7 to 1e-18 A) while moving towards higher metal work-function values. As a result of which the IOn/IOff ratio increases which leads to higher device performances.