Zsolt Miklós Kovács-Vajna

Ultra-high gain diffusion-driven organic transistor

Emerging large-area technologies based on organic transistors are enabling the fabrication of low-cost flexible circuits, smart sensors and biomedical devices. High-gain transistors are essential for the development of large-scale circuit integration, high-sensitivity sensors and signal amplification in sensing systems. Unfortunately, organic field-effect transistors show limited gain, usually of the order of tens, because of the large contact resistance and channel-length modulation. Here we show a new organic field-effect transistor architecture with a gain larger than 700. This is the highest gain ever reported for organic field-effect transistors. In the proposed organic field-effect transistor, the charge injection and extraction at the metal–semiconductor contacts are driven by the charge diffusion. The ideal conditions of ohmic contacts with negligible contact resistance and flat current saturation are demonstrated. The approach is general and can be extended to any thin-film technology opening unprecedented opportunities for the development of high-performance flexible electronics.

Robust design of low EMI susceptibility CMOS OpAmp

This paper addresses a new approach to design a CMOS operational amplifier which provides a good tradeoff between high gain and strong immunity to electromagnetic interferences. The proposed amplifier is based on two main blocks: the first is a fully differential folded cascode with modified input pair and the second is a source cross coupled AB class buffer. Thanks to the folded cascode stage and to the symmetrical output buffer, the amplifier exhibits both intrinsic robustness to interferences and good amplifier performances. The circuit was fabricated in a 0.8-/spl mu/m n-well CMOS technology (AMS CYE process). Experimental results, in terms of electromagnetic interference (EMI) immunity, are presented and successfully compared with commercial amplifiers. Measurements carried out on the chip and the amplifier overall performances are provided along with the corresponding simulation results.

Automatic Scaling Procedures for Analog Design Reuse

In this paper, a methodology for analog design reuse is proposed. The basic idea is to keep the circuit topology unchanged while automatically modifying the MOSFETs aspect ratio in order to control the transistor transconductances gm and output conductances gDS. If gms and gDSs of each transistor are kept unchanged through the scaling procedure, we show that the overall frequency behavior of the scaled circuit remains very similar to the original one. The approach is very simple and it is suitable for the scaling of analog circuits. No input and output terminals have to be defined and it can be straightforwardly implemented in an automatic scaling tool. When this approach fails, more complex iterative numerical loops may be adopted. In order to validate and compare the scaling approaches, several linear and nonlinear circuits were scaled from a 0.25-mum, 2.5-V voltage supply to a 0.15-mum, 1.2-V voltage supply in standard CMOS technologies

Quantum tunnelling and charge accumulation in organic ferroelectric memory diodes

Non-volatile memories—providing the information storage functionality—are crucial circuit components. Solution-processed organic ferroelectric memory diodes are the non-volatile memory candidate for flexible electronics, as witnessed by the industrial demonstration of a 1u2009kbit reconfigurable memory fabricated on a plastic foil. Further progress, however, is limited owing to the lack of understanding of the device physics, which is required for the technological implementation of high-density arrays. Here we show that ferroelectric diodes operate as vertical field-effect transistors at the pinch-off. The tunnelling injection and charge accumulation are the fundamental mechanisms governing the device operation. Surprisingly, thermionic emission can be disregarded and the on-state current is not space charge limited. The proposed model explains and unifies a wide range of experiments, provides important design rules for the implementation of organic ferroelectric memory diodes and predicts an ultimate theoretical array density of up to 1012u2009bitu2009cm−2.