Numerical and Analytical Modeling to Determine Performance Trade-offs in Hydrogel-based pH Sensors

Hydrogel based pH sensors are promising candidates for implantable sensors due to their low-cost and biocompatibility. Despite their commercial potential and numerous theoretical/experimental reports, the trade-offs between different performance parameters are not well understood, and explicitly stated. In this work, we develop a numerical and analytical framework to show that there is a fundamental trade-off between the performance parameters i.e. sensitivity/dynamic range vs. response-time/response-asymmetry in hydrogel sensors under constrained swelling conditions. Specifically, we consider the effect of the gel parameters, such as the ionizable group density ( Nf) and its dissociation constant ( Ka), on the sensor performance. We show that improvement of sensitivity/dynamic range leads to degradation in response time/symmetry and therefore, a compromise must be made to optimize device performance

A memory window expression to evaluate the endurance of ferroelectric FETs

The recent discovery of ferroelectricity in HfO2 has revived the interest into non-volatile memories based on ferroelectric transistors (FeFETs). The key advantages of these FeFETs include the low power consumption and the compatibility with the existing CMOS process. On the other hand, issues related mainly to endurance still represent a challenge to the development of the technology. In this Letter, we propose to exploit an analytical expression for the Memory Window (MW) as a simple yet effective characterization tool to evaluate the endurance of FeFETs. The MW is defined as the difference between threshold voltages occurring due to polarization switching. The analytical formulation of the MW allows one to quickly estimate the generated trap concentration as a function of number of writing cycles (or time) without recurring to numerical simulations. With the aid of the analytical model, we find that for typical program/erase pulse amplitudes and duration, endurance has a weak dependence on writing conditions. The characterization technique based on the MW would allow the systematic comparison of the performance and endurance of next-generation FeFETs

Thermodynamic efficiency limits of classical and bifacial multi-junction tandem solar cells: An analytical approach

Bifacial tandem cells promise to reduce three fundamental losses (i.e., above-bandgap, below bandgap, and the uncollected light between panels) inherent in classical single junction photovoltaic (PV) systems. The successive filtering of light through the bandgapcascade and the requirement of current continuity make optimization of tandem cellsdifficult and accessible only to numerical solution through computer modeling. The challenge is even more complicated for bifacial design. In this paper, we use an elegantly simple analytical approach to show that the essential physics of optimization is intuitively obvious, and deeply insightful results can be obtained with a few lines of algebra. This powerful approach reproduces, as special cases, all of the known results of conventional and bifacial tandem cells and highlights the asymptotic efficiency gain of these technologies