Benjamin Grisafe

Performance benchmarking of p-type In 0.65 Ga 0.35 As/GaAs 0.4 Sb 0.6 and Ge/Ge 0.93 Sn 0.07 hetero-junction tunnel FETs

We experimentally demonstrate and benchmark the performance of p-channel TFETs (PTFETs) comparing Group III-V (In<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs<inf>0.4</inf>SW<inf>0.6</inf>) against Group IV (Ge/Ge<inf>0.93</inf>Sn<inf>0.07</inf>) semiconductor hetero-junctions. This is enabled via gate stack engineering with extremely scaled dielectrics achieving the highest accumulation capacitance density (≥3μF/cm²) on both GaAs<inf>0.4</inf>Sb<inf>0.6</inf> and Ge<inf>0.88</inf>Sn<inf>0.12</inf> channels, respectively. Temperature and electric field dependent I-V measurements coupled with first-principles density functional theory (DFT) based band-structure calculations and analytical modeling based on modified Shockley-Read-Hall formalism, are used to quantify contributions to carrier transport from band-to-band tunneling and trap-assisted tunneling (TAT). GeSn based PTFETs are found to outperform In<inf>0.65</inf>Ga<inf>0.35</inf>As/GaAs<inf>0.4</inf>Sb<inf>0.6</inf> PTFETs benefiting from band-gap engineering (higher I<inf>on</inf>) and reduced phonon assisted TAT current (lower D<inf>it</inf>).

Ag/HfO 2 based threshold switch with extreme non-linearity for unipolar cross-point memory and steep-slope phase-FETs

We demonstrate a novel Ag/HfO2 based threshold switch (TS) with a selectivity∼107, a high ON-state current (Ion) of 100 μA, and ∼10pA leakage current. The thresholding characteristics of the TS result from electrically triggered spontaneous formation and rupture of an Ag filament which acts an interstitial dopant in the HfO2 insulating matrix. Further, we harness the extreme non-linearity of the TS in (1) Selectors for Phase Change Memory (PCM) based cross-point memory. We show through array level simulations of a 1024kb memory, a read margin of 28% and write margin of 32% for a leakage power of <25μW (V/3 scheme); (2) A steep-slope sub-kT/q Phase-FET, experimentally demonstrating a switching-slope (SS) of 3mV/decade (over 5 orders of Ids), and >10x Ion improvement over the conventional FET (at iso-Ioff) at T=90C (50x at T=25C); making this a promising TS for both emerging memory, and steep-slope transistor applications.

Electrically triggered insulator-to-metal phase transition in two-dimensional (2D) heterostructures

We evaluate the heterogeneous integration of the layered correlated electron material, 1T-TaS2, on semiconducting 2H-MoS2 for the realization of an all two-dimensional insulator-to-metal (IMT) phase transition device. First principles calculations investigate the band structure of the resulting heterostructure and confirm the existence of a charge density wave (CDW)-based bandgap. 1T-TaS2 films are synthesized via powder vapor deposition on monolayer MoS2 substrates and shown to exhibit CDW induced IMT phase transitions. Both Raman and electrical measurements display reversible commensurate to nearly commensurate CDW IMT phase transitions. Finally, a phase transition transistor device is demonstrated that harnesses the electrically triggered abrupt IMT in 1T-TaS2 and semiconducting properties of 2H-MoS2.We evaluate the heterogeneous integration of the layered correlated electron material, 1T-TaS2, on semiconducting 2H-MoS2 for the realization of an all two-dimensional insulator-to-metal (IMT) phase transition device. First principles calculations investigate the band structure of the resulting heterostructure and confirm the existence of a charge density wave (CDW)-based bandgap. 1T-TaS2 films are synthesized via powder vapor deposition on monolayer MoS2 substrates and shown to exhibit CDW induced IMT phase transitions. Both Raman and electrical measurements display reversible commensurate to nearly commensurate CDW IMT phase transitions. Finally, a phase transition transistor device is demonstrated that harnesses the electrically triggered abrupt IMT in 1T-TaS2 and semiconducting properties of 2H-MoS2.

A steep slope Phase-FET based on 2D MoS 2 and the electronic phase transition in VO 2

Two-dimensional materials are being investigated for potential nanoelectronic applications such as transistors for scaled technology nodes. Here we investigate the possibility of further augmenting the performance of such 2D materials through a novel device concept known as the hybrid-phase transition FET or Phase-FET. The MoS2 based Phase-FET incorporates an insulator-to-metal transition material VO2 integrated in series with the source of a MOSFET, which provides an internal amplification across the insulator-to-metal transition and results in steep slope switching.

Ultra-low power probabilistic IMT neurons for stochastic sampling machines

Stochastic sampling machines (SSM) utilize neural sampling from probabilistic spiking neurons to escape local minima and prevent overfitting of training datasets [1]. This enables improved error rates compared to deterministic implementations, and, in turn, enables lower bit precision, decreased chip area, and reduced energy consumption. In this work, we experimentally demonstrate: (i) Insulator-to-Metal Phase Transition (IMT) neurons with record low peak operating power of 11.9μW at V DD =0.7V; (ii) the IMT in vanadium dioxide (VO2) provides a natural probabilistic hardware substrate for realizing a compact stochastic IMT neuron for SSMs; (iii) implementation of SSM for pattern recognition on MNIST database [2] using experimentally calibrated device modeling. These results are compared to a 22nm CMOS ASIC which shows stochastic IMT neuron based SSMs result in a 4.5x reduction in system power consumption.