Shifting the frontiers of analog and mixed-signal electronics

Nowadays, analog and mixed-signal (AMS) IC designs, mainly found in the frontends of large ICs, are highly dedicated, complex, and costly. They form a bottleneck in the communication with the outside world, determine an upper bound in quality, yield, and flexibility for the IC, and require a significant part of the power dissipation. Operating very close to physical limits, serious boundaries are faced. This paper relates, from a high-level point of view, these boundaries to the Shannon channel capacity and shows how the AMS circuitry forms a matching link in transforming the external analog signals, optimized for the communication medium, to the optimal on-chip signal representation, the digital one, for the IC medium. The signals in the AMS part itself are consequently not optimally matched to the IC medium. To further shift the frontiers of AMS design, a matching-driven design approach is crucial for AMS. Four levels will be addressed: technology-driven, states-driven, redundancy-driven, and nature-driven design. This is done based on an analysis of the various classes of AMS signals and their specific properties, seen from the angle of redundancy. This generic, but abstract way of looking at the design process will be substantiated with many specific examples

Organic thin-film transistors:from technologies to circuits

Organic molecules (i.e. carbon-based) have opened a new and rapidly-growing industrial field in the optoelectronic market bringing to this field a new dimension of thinness and flexibility. In this context, this thesis has focused on one particular building block of the vast and emerging field of organic electronics: the organic thin-film transistor (OTFT) which uses organic compounds as semiconductor. Whereas the OTFT-based circuits are not meant to compete with the silicon-based high-end industry (micro-processors...), their performance have already reached levels enabling their use in potential applications such as displays (e-paper, LCD, OLED) or radiofrequency identification (RFID) tags. The continuously growing number of available organic molecules exhibiting conductive, semi-conductive or insulating properties combined with the number of available deposition/patterning methods (e.g. gravure printing) gives more flexibility to the technology. These additional degrees of freedom raise two main questions: How to identify the most suitable OTFT platform for a given application and how to estimate its potential, as for instance in, of digital circuits? This thesis targets to answer to those questions. For this purpose, several OTFT platforms have been screened and their performance have been discussed and compared through standard figures of merit. The self-aligned nano-imprinted technology has demonstrated state-of-the-art sub-micrometer OTFTs on 4-inch flexible substrates. This made this platform the most suitable candidate for developing the potential evaluation framework. For that purpose, a static model suitable for the sub-micrometer OTFTs has been developed which embeds almost all known electrical aspects of OTFTs. Then the device-to-device discrepancy often observed in OTFTs has been studied and statistical modeling methods introduced. This allowed the simulation of sub-micrometer inverters performed with commercially available tools. Next, a statistical method has been developed to evaluate the potential of the sub-micrometer OTFTs for digital applications. Whereas the method concludes that these sub-micrometer OTFTs are not mature enough to make complex digital circuits, this methodology is technology-independent and may thus serve as a basis to characterize unipolar-logic printed electronics and be further extended to complementary-logic circuits. Last but not least, an automation effort has been undergone all along this thesis in order to increase the throughput for such demanding data analysis. The main outcome of this task is a user-friendly multi-analysis and parameter extraction platform

Investigation of Variation in Organic Thin-film Transistors (OTFT) and Design of Variation-aware Organic Circuits

This work investigates the key sources of variability in OTFT namely process variations and bias-stress induced variation, and presents circuit design techniques to build robust variation-aware digital and analog circuits using OTFT. OTFT suffer from a relatively large Vt variation due to the bias stress effects, and process mismatch variations. Though these effects are also prevalent in silicon based transistors, their magnitude is comparatively larger in the case of OTFT. This renders the well-established silicon based circuits unsuitable for organic electronics. Therefore, direct adaptation of the silicon based circuits for realising organic circuits does not effectively handle the relatively large parameter and mismatch variations associated with OTFT. In this work, we first investigate the bias-stress induced threshold voltage (Vt) variation and process variations to understand the impact of these variations on the performance of organic circuits. Then, two different strategies were employed to design robust organic circuits. The first method involves designing new load topologies that are more robust to the threshold voltage variations without compromising on gain. The other strategy was to realize the essential analog circuit functionalities like comparator, ADC using digital circuit blocks. In this direction, a digital comparator and digital A/D converter circuits were developed. Finally to demonstrate the system integration, a temperature sensing organic smart label system was designed

A tunable transconductor for analog amplification and filtering based on double-gate organic TFTs

This paper presents a transconductor designed using a physical model of double-gate p-type organic thin film transistors (OTFTs). A control voltage can be used to vary the output resistance and the transconductance over one order of magnitude. The voltage gain does not depend on process parameters and therefore is insensitive to shelf and operational degradation. This circuit can be used as a tunable resistor, in voltage amplifiers or in GmC filters

A tunable transconductor for analog amplification and filtering based on double-gate organic TFTs

This paper presents a transconductor designed using a physical model of double-gate p-type organic thin film transistors (OTFTs). A control voltage can be used to vary the output resistance and the transconductance over one order of magnitude. The voltage gain does not depend on process parameters and therefore is insensitive to shelf and operational degradation. This circuit can be used as a tunable resistor, in voltage amplifiers or in GmC filters