A multi-level capacitor-less memory cell was fabricated with a fully depleted n-metal-oxide-semiconductor field-effect transistor on a nano-scale strained silicon channel on insulator (FD sSOI n-MOSFET). The 0.73% biaxial tensile strain in the silicon channel of the FD sSOI n-MOSFET enhanced the effective electron mobility to ∼ 1.7 times that with an unstrained silicon channel. This thereby enables both front- and back-gate cell operations, demonstrating eight-level volatile memory-cell operation with a 1 ms retention time and 12 µA memory margin. This is a step toward achieving a terabit volatile memory cell.
We investigated the dependence of Cap-less memory on top of silicon with a thickness between 15.5 and 72.3 nm. It was confirmed that the memory margin depends on the impact ionization rate associated with the increased conduction current density and the decreased lateral electric field as the top silicon thickness increases. In particular, we observed that the maximum memory margin is 61 A at a 45 nm top silicon thickness, where the impact ionization rate is maximized. Consequently, we obtained the optimal top silicon thickness of 45 nm for Cap-less memory cells operating in fully depleted silicon-on-insulator n-metal-oxide-semiconductor field-effect transistors.
We investigated through a theoretical simulation how the phonon-limited electron mobility in both (110)- and (100)-oriented ultrathin-body (UTB) silicon-on-insulator (SOI) n-metal-oxide-semiconductor field-effect transistors (MOSFETs) depends on the top silicon thickness within a range from 20to2nm. No electron mobility enhancement was observed in (110) UTB SOI n-MOSFETs when the top silicon thickness was around 5nm, unlike in (100) UTB n-MOSFETs. Thus, electron mobility in (110) UTB SOI n-MOSFETs decreased with top silicon thickness, particularly in the range below 10nm. We attributed the electron mobility degradation in (110) UTB SOI n-MOSFETs within the top silicon thickness range below 10nm to a decrease in the effective width of the inversion layer and an increase in intravalley acoustic phonon scattering, rather than to less carrier repopulation due to less band splitting between two- and fourfold valleys.
We study the kinetics of a search of a single fixed target by a large number of searchers performing an intermittent biased random walk in a homogeneous medium. Our searchers carry out their walks in one of two states between which they switch randomly. One of these states (search phase) is a nearest-neighbor walk characterized by the probability of stepping in a given direction (i.e. the walks in this state are not necessarily isotropic). The other (relocation phase) is characterized by the length of the jumps (i.e. when in this state a walker does not perform a nearest-neighbor walk). Within such a framework, we propose a model to describe the searchers' dynamics, generalizing results of our previous work. We have obtained, and numerically evaluated, analytic results for the mean number of distinct sites visited up to a maximum evolution time. We have studied the dependence of this quantity on both the transition probability between the states and the parameters that characterize each state. In addition to our theoretical approach, we have implemented Monte Carlo simulations, finding excellent agreement between the theoretical-numerical and simulations results.
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