High Performance Modulation of High-Frequency AC Link Inverter

Inverters with high voltage conversion ratio are used in systems with sources such as batteries, photovoltaic (PV) modules or fuel cells. Transformers are often used in such inverters to provide the required voltage conversion ratio and isolation. In this paper, a compact high-frequency (HF) transformer interfaced AC link inverter with lossless snubber is discussed. A high performance synchronized modulation scheme is proposed for this inverter. This modulation addresses the issue of over-voltage spikes due to transformer leakage inductance and it is shown that the circuit can operate safely even when the turn-on delay, such as dead-time, is not used in the HF rectifier section. The problem of spurious turn-on in the HF inverter switches is also mitigated by the proposed modulation method. The circuit performance is validated experimentally with a $900W$ prototype inverter.

Critical investigation of high performance spin-coated high-kappa titania thin films based MOS capacitor

We report the tunable dielectric constant of titania films with low leakage current density. Titanium dioxide (TiO2) films of three different thicknesses (36, 63 and 91 nm) were deposited by the consecutive steps of solution preparation, spin-coating, drying, and firing at different temperatures. The problem of poor adhesion between Si substrate and TiO2 insulating layer was resolved by using the plasma activation process. The surface roughness was found to increase with increasing thickness and annealing temperature. The electrical investigation was carried out using metal-oxide-semiconductor structure. The flat band voltage (V-FB), oxide trapped charge (Q(ot)), dielectric constant (kappa) and equivalent oxide thicknesses are calculated from capacitance-voltage (C-V) curves. The C-V characteristics indicate a thickness dependent dielectric constant. The dielectric constant increases from 31 to 78 as thickness increases from 36 to 91 nm. In addition to that the dielectric constant was found to be annealing temperature and frequency dependent. The films having thickness 91 nm and annealed at 600 A degrees C shows the low leakage current density. Our study provides a broad insight of the processing parameters towards the use of titania as high-kappa insulating layer, which might be useful in Si and polymer based flexible devices.

High performance nanocomposite thin film transistors with bilayer carbon nanotube-polythiophene active channel by ink-jet printing

Nanocomposite thin film transistors (TFTs) based on nonpercolating networks of single-walled carbon nanotubes (CNTs) and polythiophene semiconductor [poly [5, 5′ -bis(3-dodecyl-2-thienyl)- 2, 2′ -bithiophene] (PQT-12)] thin film hosts are demonstrated by ink-jet printing. A systematic study on the effect of CNT loading on the transistor performance and channel morphology is conducted. With an appropriate loading of CNTs into the active channel, ink-jet printed composite transistors show an effective hole mobility of 0.23 cm 2 V-1 s-1, which is an enhancement of more than a factor of 7 over ink-jet printed pristine PQT-12 TFTs. In addition, these devices display reasonable on/off current ratio of 105-10 6, low off currents of the order of 10 pA, and a sharp subthreshold slope (<0.8 V dec-1). The work presented here furthers our understanding of the interaction between polythiophene polymers and nonpercolating CNTs, where the CNT density in the bilayer structure substantially influences the morphology and transistor performance of polythiophene. Therefore, optimized loading of ink-jet printed CNTs is crucial to achieve device performance enhancement. High performance ink-jet printed nanocomposite TFTs can present a promising alternative to organic TFTs in printed electronic applications, including displays, sensors, radio-frequency identification (RFID) tags, and disposable electronics. © 2009 American Institute of Physics.