Tamal Mukherjee

Single-chip computers with microelectromechanical systems-based magnetic memory (invited)

This article describes an approach for implementing a complete computer system (CPU, RAM, I/O, and nonvolatile mass memory) on a single integrated-circuit substrate (a chip)—hence, the name “single-chip computer.” The approach presented combines advances in the field of microelectromechanical systems (MEMS) and micromagnetics with traditional low-cost very-large-scale integrated circuit style parallel lithographic manufacturing. The primary barrier to the creation of a computer on a chip is the incorporation of a high-capacity [many gigabytes (GB)] re-writable nonvolatile memory (in today’s terminology, a disk drive) into an integrated circuit (IC) manufacturing process. This article presents the following design example: a MEMS-based magnetic memory that can store over 2 GB of data in 2 cm2 of die area and whose fabrication is compatible with a standard IC manufacturing process.

Emerging simulation approaches for micromachined devices

In this survey paper, we describe and contrast three different approaches for extending circuit simulation to include micromachined devices. The most commonly used method, that of using physical insight to develop parameterized macromodels, is presented first. The issues associated with fitting the parameters to simulation data while incorporating design attribute dependencies are considered. The numerical model order reduction approach to macromodeling is presented second, and some of the issues associated with fast solvers and model reduction are summarized. Lastly, we describe the recently developed circuit-based approach for simulating micromachined devices, and describe the design hierarchy and the use of a catalog of parts.

Structured design of microelectromechanical systems

In order to efficiently design complex microelectromechanicalsystems (MEMS) having large numbers of multi-domain components,a hierarchically structured design approach that iscompatible with standard IC design is needed. A graphical-basedschematic, or structural, view is presented as a geometrically intuitiveway to represent MEMS as a set of interconnected lumped-parameterelements. An initial library focuses on suspended-MEMStechnology from which inertial sensors and other mechanicalmechanisms can be designed. The schematic representationhas a simulation interface enabling the designer to simulate thedesign at the component level. Synthesis of MEMS cells for commontopologies provides the system designer with rapid, optimizedcomponent layout and associated macro-models. Asynthesis module is developed for the popular folded-flexuremicromechanical resonator topology. The algorithm minimizes acombination of total layout area and voltage applied to the electromechanicalactuators. Synthesis results clearly show the designlimits of behavioral parameters such as resonant frequency for afixed process technology.

CMOS-MEMS resonant RF mixer-filters

An integrated CMOS-MEMS micromechanical resonant mixer-filter with potential for application in a single chip receiver is introduced. Air and anchor damping characterization show quality factor greater than 1500. Downconversion and filtering of signal frequencies as high as 3.2 GHz is achieved. This is the highest signal frequency applied so far to MEMS mixer-filters. Analytical calculations match well with the experimental measurements and are used to show that 0 dB mixer conversion loss is achievable. Co-simulation of the MEMS mixer with readout electronics identifies potential solutions to eliminate mixing feedthrough.

Optimization-based synthesis of microresonators

The rapid layout synthesis of microresonators from high-level engineering specifications is demonstrated. Functional parameters such as resonant frequency, quality factor, and displacement amplitude at resonance are satisfied while simultaneously minimizing a user-specified objective function. A synthesis tool implementing the optimization-based formulation can be used to explore micromechanical design issues and objectives, as illustrated with a polysilicon lateral resonator example modeled in three mechanical degrees of freedom. Layouts for four sets of five different resonators from 3 kHz to 300 kHz are generated, with each set globally optimized to minimize either active device area, electrostatic drive voltage, a weighted combination of area and drive voltage, or to maximize displacement amplitude at resonance.

Automated optimal synthesis of microresonators

The rapid layout synthesis of a microresonator from high-level functional specifications and design constraints is demonstrated. Functional parameters such as resonant frequency, quality factor, and displacement amplitude at resonance are satisfied while simultaneously minimizing an objective function. The optimal synthesis tool allows exploration of micromechanical design issues and objectives, as illustrated with a polysilicon lateral resonator example modeled in three mechanical degrees-of-freedom. Layouts for three sets of five different resonators from 3 kHz to 300 kHz are generated, with each set globally optimized to minimize either active device area, electrostatic drive voltage, or a weighted combination of area and drive voltage.

Systematic modeling of microfluidic concentration gradient generators

This paper presents a systematic modeling methodology for microfluidic concentration gradient generators. The generator is decomposed into a system of microfluidic elements with relatively simple geometries. Parameterized models for such elements are analytically developed and hold for general sample concentration profiles and arbitrary flow ratios at the element inlet; hence, they are valid for concentration gradient generators that rely on either complete or partial mixing. The element models are then linked through an appropriate set of parameters embedded at the element interfaces. This yields a systematic, lumped-parameter representation of the entire generator in terms of a network of gradient-generation elements. The system model is verified by numerical analysis and experimental data and accurately captures the overall effects of network topologies, element sizes, flow rates and reservoir sample concentrations on the generation of sample concentration gradient. Finally, this modeling methodology is applied to propose a novel and compact microfluidic device that is able to create concentration gradients of complex shapes by juxtaposing simple constituent profiles along the channel width.

A model for laminar diffusion-based complex electrokinetic passive micromixers.

This paper presents a model for the efficient and accurate simulations of laminar diffusion-based complex electrokinetic passive micromixers by representing them as a system of mixing elements of relatively simple geometry. Parameterized and analytical models for such elements are obtained, which hold for general sample concentration profiles and arbitrary flow ratios at the element inlet. A lumped-parameter and system-level model is constructed for a complex micromixer, in which the constituent mixing elements are represented by element models, in such a way that an appropriate set of parameters are continuous at the interface between each pair of adjacent elements. The system-level model, which simultaneously computes electric circuitry and sample concentration distributions in the entire micromixer, agrees with numerical and experimental results, and offers orders-of-magnitude improvements in computational efficiency over full numerical simulations. The efficiency and usefulness of the model is demonstrated by exploring a number of laminar diffusion based mixers and mixing networks that occur in practice.

Efficient handling of operating range and manufacturing line variations in analog cell synthesis

We describe a synthesis system that takes operating range constraints and inter and intracircuit parametric manufacturing variations into account while designing a sized and biased analog circuit. Previous approaches to computer-aided design for analog circuit synthesis have concentrated on nominal analog circuit design, and subsequent optimization of these circuits for statistical fluctuations and operating point ranges. Our approach simultaneously synthesizes and optimizes for operating and manufacturing variations by mapping the circuit design problem into an infinite programming problem and solving it using an annealing within annealing formulation. We present circuits designed by this integrated synthesis system, and show that they indeed meet their operating range and parametric manufacturing constraints. And finally, we show that our consideration of variations during the initial optimization-based circuit synthesis leads to better starting points for post-synthesis yield optimization than a classical nominal synthesis approach.

Tunable RF and analog circuits using on-chip MEMS passive components

Micromachining in RF foundry processes enhances inductor and capacitor quality factors, increases varactor tuning range, and supports creation of electromechanical mixer-filters that downconvert RF signals from GHz to MHz frequency band with built-in frequency selectivity. An on-chip parallel receiver architecture and circuit blocks incorporating these MEMS devices for low-power operation are presented.