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Discrepancies exist between the theoretically predicted and experimentally measured performance of band-to-band tunneling devices, such as Esaki diodes and tunnel field-effect transistors (TFETs). We resolve this discrepancy for highly-doped, direct-bandgap Esaki diodes by successfully calibrating a semi-classical model for high-doping-induced ballistic band-tails tunneling currents at multiple temperatures with two In0.53Ga0.47As Esaki diodes using their SIMS doping profiles, C-V characteristics and their forward-bias current density in the negative differential resistance (NDR) regime. The current swing in the NDR regime is shown not to be linked to the band-tails Urbach energy. We further demonstrate theoretically that the calibrated band-tails contribution is also the dominant band-tails contribution to the subthreshold swing of the corresponding TFETs. Lastly, we verify that the presented procedure is applicable to all direct-bandgap semiconductors by successfully applying it to InAs Esaki diodes in literature.

Dopant pockets in combination with a III-V heterostructure have become a staple in simulations of tunnel field-effect transistors (TFET) to achieve acceptable on-currents (ION) and to break the ION-subthreshold swing trade-off in pTFETs. Questions on the scalability and variability of these dopant pockets remain, however. We therefore propose an alternative concept using two opposite sheet charges at the tunnel junction that are realized by exploiting different bonding types. With fully quantum mechanical 30-band k.p-based simulations, we investigate two configurations that exhibit such sheet charges both at the device level and in a ring-oscillator: a lattice-matched GaAs-Ge-GaAs heterostructure TFET and a homostructure InGaAs TFET. By comparing to pocketed broken gap GaSb-InAs TFETs, we show that built-in sheet charge is a valid alternative for both nTFET and pTFET, with the prospect of lower variability and better scalability.

2-D transition metal dichalcogenides (TMDs) are promising materials for CMOS application due to their ultrathin channel with excellent electrostatic control. TMDs are especially well suited for tunneling field-effect transistors (TFETs) due to their low-dielectric constant and their promise of atomically sharp and self-passivated interfaces. Here, we experimentally demonstrate band-to-band tunneling (BTBT) in Van der Waals heterostructures formed by MoS2 and MoTe2. Density functional theory simulations of the band structure show our MoS2-MoTe2 heterojunctions have a staggered band alignment, which boosts BTBT compared to a homojunction configuration. Low-temperature measurements and electrostatic simulations provide understanding toward the role of Schottky contacts and the material thickness on device performance. Negative differential transconductance-based devices were also demonstrated using a different device architecture. This paper provides the prerequisites and challenges required to overcome at the contact region to achieve a steep subthreshold slope and high ON-currents with 2-D-based TFETs.

For nanometer MOSFETs, charging and discharging a single trap induces random telegraph noise (RTN). When there are more than a few traps, RTN signal becomes complex and appears as within a device fluctuation (WDF). RTN/WDF causes jitters in switch timing and is a major challenge to low power circuits. In addition to RTN/WDF, devices also age. The interaction between RTN/WDF and aging is of importance and not fully understood. Some researchers reported aging increasing RTN/WDF, while others showed RTN/WDF being hardly affected by aging. The objective of this paper is to investigate the impact of hot carrier aging (HCA) on the RTN/WDF of nMOSFETs. For devices of average RTN/WDF, it is found that the effect of HCA is generally modest. For devices of abnormally high RTN/WDF, however, for the first time, we report HCA reducing RTN/WDF substantially (>50%). This reduction originates from either a change of current distribution or defect losses.

STT-MRAM is a promising non-volatile memory for high speed applications. The thermal stability factor (Δ = Eb/kT) is a measure for the information retention time, and an accurate determination of the thermal stability is crucial. Recent studies show that a significant error is made using the conventional methods for Δ extraction. We investigate the origin of the low accuracy. To reduce the error down to 5%, 1000 cycles or multiple ramp rates are necessary. Furthermore, the thermal stabilities extracted from current switching and magnetic field switching appear to be uncorrelated and this cannot be explained by a macrospin model. Measurements at different temperatures show that self-heating together with a domain wall model can explain these uncorrelated Δ. Characterizing self-heating properties is therefore crucial to correctly determine the thermal stability.

The reconfigurable physically unclonable function (PUF) is an advanced security hardware primitive, suitable for applications requiring key renewal or similar refresh functions. The Oxygen vacancies-based resistive RAM (RRAM), has been claimed to be a physically reconfigurable PUF due to its intrinsic switching variability. This paper first analyzes and compares various previously published RRAM-based PUFs with a physics-based RRAM model. We next discuss their possible reconfigurability assuming an ideal configuration-to-configuration behavior. The RRAM-to-RRAM variability, which mainly originates from a variable number of unremovable vacancies inside the RRAM filament, however, has been observed to have significant impact on the reconfigurability. We show by quantitative analysis on the clear uniqueness degradation from the ideal situation in all the discussed implementations. Thus we conclude that true reconfigurability with RRAM PUFs might be unachievable due to this physical phenomena.

Perpendicular magnetic anisotropy (PMA) is an essential condition for CoFe thin films used in magnetic random access memories. Until recently, interfacial PMA was mainly known to occur in materials stacks with MgO\CoFe(B) interfaces or using an adjacent crystalline heavy metal film. Here, PMA is reported in a CoFeB\Ta bilayer deposited on amorphous high-κ dielectric (relative permittivity κ=20) HfO2, grown by atomic layer deposition (ALD). PMA with interfacial anisotropy energy Ki up to 0.49 mJ/m2 appears after annealing the stacks between 200°C and 350°C, as shown with vibrating sample magnetometry. Transmission electron microscopy shows that the decrease of PMA starting from 350°C coincides with the onset of interdiffusion in the materials. High-κ dielectrics are potential enablers for giant voltage control of magnetic anisotropy (VCMA). The absence of VCMA in these experiments is ascribed to a 0.6 nm thick magnetic dead layer between HfO2 and CoFeB. The results show PMA can be easily obtained on ALD high-κ dielectrics.