InGaAs/GaAsSb type-two heterojunction vertical tunnel-FETs

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 59-62).The supply voltage (VDD) scaling of conventional CMOS technology is approaching its limit due to the physical limit of 60 mV/dec subthreshold swing (SS) at room temperature and the requirement for controlled leakage current. In order to continue VDD scaling for low power applications, novel device structures with steep SS have been proposed. Tunnel-FETs (TFETs) are among the most attractive device structure due to their compatibility with conventional CMOS technology and the potential for outstanding VDD scalability. Heterostructure vertical TFETs with enhanced gate modulation promise significantly improved electrostatic control and drive current relative to lateral tunneling designs. In this thesis, vertical TFETs based on InGaAs/GaAsSb heterostructure are investigated in terms of design, fabrication and electrical characterization. Ino.53Gao.47As/ GaAso.5Sb0.5 heterostructure vertical TFETs are fabricated with an airbridge structure, designed to prevent parasitic tunneling path in the device, with a two-step highly selective undercut process. Electrical measurement of the devices with various gate areas demonstrates area-dependent tunneling current. The Ino.53Gao.47As/ GaAs0 .5 Sb. 5 vertical TFETs with HfO2 high-k gate dielectric (EOT ~ 1.3 nm) exhibit minimum sub-threshold swings of 140 and 58 mV/dec at 300 and 150 K respectively, with an ON-current density of 0.5 [mu]A/[mu]m2 at VDD = 0.5 V at 300 K. A physical model of TFET operation in the ON-state is proposed based on temperature dependent measurements, which reveal a current barrier due to an ungated region near the drain. Simulations illustrate that the gate-to-drain distance must be scaled to eliminate this barrier. In diode-mode operation, outstanding backward diode performance is demonstrated in this system for the first time, with gate-tunable curvature coefficient of 30 V1 near VDS= 0 V. These results indicate the potential of vertical TFETs in hybrid IC applications.by Tao Yu.S.M

Intraperitoneal delivery of paclitaxel by poly(ether-anhydride) microspheres effectively suppresses tumor growth in a murine metastatic ovarian cancer model

Intraperitoneal (IP) chemotherapy is more effective than systemic chemotherapy for treating advanced ovarian cancer, but is typically associated with severe complications due to high dose, frequent administration schedule, and use of non-biocompatible excipients/delivery vehicles. Here, we developed paclitaxel (PTX)-loaded microspheres composed of di-block copolymers of poly(ethylene glycol) and poly(sebacic acid) (PEG-PSA) for safe and sustained IP chemotherapy. PEG-PSA microspheres provided efficient loading (∼13 % w/w) and prolonged release (∼13 days) of PTX. In a murine ovarian cancer model, a single dose of IP PTX/PEG-PSA particles effectively suppressed tumor growth for more than 40 days and extended the median survival time to 75 days compared to treatments with Taxol® (47 days) or IP placebo particles (34 days). IP PTX/PEG-PSA was well tolerated with only minimal to mild inflammation. Our findings support PTX/PEG-PSA microspheres as a promising drug delivery platform for IP therapy of ovarian cancer and potentially other metastatic peritoneal cancers

InGaAs/GaAsSb quantum-well Tunnel-FETs for ultra-low power applications

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016.Cataloged from PDF version of thesis.Includes bibliographical references.The Tunnel-FET (TFET), where carrier injection is determined by gate-controlled tunneling from the source to the channel, has been attractive as one of the promising candidates for future ultra-low power applications. In this thesis, inline-TFETs with tunneling direction aligned to the gate electric field are designed, fabricated and analyzed based on InGaAs/GaAsSb material. Using ultrathin InGaAs/GaAsSb quantum-well (QW), the device fabrication technology was developed and the tunneling properties of two successive generations of QWTFETs were investigated. In the first generation QWTFETs, the limitation of gate oxide quality on InGaAs and parasitic thermal currents manifests itself in degraded subthreshold swing (SS) of 140 mV/dec, as well as strongly temperature dependent SS from 300 K to 77 K. The second generation QWTFETs with sub-nm InP cap between gate oxide and InGaAs channel and revised structure design has demonstrated improved SS of 87 mV/dec at 300 K and temperature independent SS below 140 K, indicating the achievable tunneling current steepness with the current device design. Physical modeling and quantum simulations based on the low temperature I-V characteristics were used to analyze the fundamental gate efficiency of the experimental QWTFETs in order to reveal the ultimate intrinsic tunneling steepness of the InGaAs/GaAsSb tunneling junction. The extracted gate efficiency around 55-64% is due to the coupling of the gate capacitance and tunneling junction capacitance and degrades dramatically the attainable SS in the QWTFET. On the other hand, the implied intrinsic tunneling steepness of the InGaA/GaAsSb is around 30 mV/dec, almost identical to previously reported non-abruptness of the conduction/valence band-edge into the bandgap. The result indicates the possibility of achieving SS as low as 38 mV/dec in QWTFETs by improving gate efficiency by up to 78% with proposed optimized parameters based on simulation results. Non-logic TFET-specific circuits are also explored to understand the advantage of TFETs in real-world applications. Due to the superior nonlinearity in the device I-V characteristics and gate-dependent negative-differential-resistance (NDR) under forward bias condition (VDS < 0), experimental and simulation results of QWTFET-based RF detector, oscillator and mixer have demonstrated the potential of QWTFET in these non-logic circuit applications, especially for ultralow standby power applications.by Tao Yu.Ph. D