Metal oxide-based monolithic complementary metal oxide semiconductor gas sensor microsystem

A fully integrated gas sensor microsystem is presented, which comprises for the first time a micro hot plate as well as advanced analog and digital circuitry on a single chip. The micro hot plate is coated with a nanocrystalline SnO2 thick film. The sensor chip is produced in an industrial 0.8-microm CMOS process with subsequent micromachining steps. A novel circular micro hot plate, which is 500 x 500 microm(2) in size, features an excellent temperature homogeneity of +/-2% over the heated area (300-microm diameter) and a high thermal efficiency of 6.0 degrees C/mW. A robust prototype package was developed, which relies on standard microelectronic packaging methods. Apart from a microcontroller board for managing chip communication and providing power supply and reference signals, no additional measurement equipment is needed. The on-chip digital temperature controller can accurately adjust the membrane temperature between 170 and 300 degrees C with an error of +/-2 degrees C. The on-chip logarithmic converter covers a wide measurement range between 1 kOmega and 10 MOmega. CO concentrations in the sub-parts-per-million range are detectable, and a resolution of +/-0.1 ppm CO was achieved, which renders the sensor capable of measuring CO concentrations at threshold levels.     

Microfabrication techniques for chemical/biosensors

Microfabrication processes for chemical and biochemical sensors are reviewed. Standard processing steps originating from semiconductor technology are detailed, and specific micromachining steps to fabricate three-dimensional mechanical structures are described. Fundamental chemical sensor principles are briefly abstracted and corresponding state-of-the-art examples of microfabricated chemical sensors and biosensors are given. The advantages and disadvantages of either fabricating devices in IC fabrication technology with additional microfabrication steps, or of using custom-designed nonstandard microfabrication process flows are debated. Finally, monolithic integrated chemical and biological microsensor systems are presented, which include transducer structures and operation circuitry on a single chip.     

Detection and discrimination capabilities of a multitransducer single-chip gas sensor system

The performance of a single-chip, three-transducer, complementary metal oxide semiconductor gas sensor microsystem has been thoroughly evaluated. The monolithic gas sensor system includes three polymer-coated transducers, a mass-sensitive cantilever, a thermoelectric calorimetric sensor, and an interdigitated capacitive sensor that are integrated along with all electronic circuits needed to operate these sensors. The system additionally includes a temperature sensor and a serial interface unit so that it can be directly connected to, for example, a microcontroller. Several multitransducer chips have been coated with various partially selective polymers and then have been exposed to different volatile organic compounds. The sensitivities of the three different polymer-coated transducers to defined sets of gaseous analytes have been determined. The obtained sensitivity values have then been normalized with regard to the partition coefficients of the respective analyte/polymer combination to reveal the transducer-specific effects. The results of this investigation show that the three different transducers respond to fundamentally different molecular properties, such as the analyte molecular mass (mass-sensitive), its dielectric coefficient (capacitive), and its sorption heat (calorimetric) so that correlations between the determined sensitivity values and the different molecular properties of the absorbed analytes could be established. The information as provided by the system, hence, represents a body of orthogonal data that can serve as input to appropriate signal processing and pattern recognition techniques to address issues such as the quantification of analytes in mixtures.     

Magnetically actuated complementary metal oxide semiconductor resonant cantilever gas sensor systems

In the present paper, an electromagnetically actuated resonant cantilever gas sensor system is presented that features piezoresistive readout by means of stress-sensitive MOS transistors. The monolithic gas sensor system includes a polymer-coated resonant cantilever and the necessary oscillation feedback circuitry, both monolithically integrated on the same chip. The fully differential feedback circuit allows for operating the device in self-oscillation with the cantilever constituting the frequency-determining element of the feedback loop. The combination of magnetic actuation and transistor-based readout entails little power dissipation on the cantilever and reduces the temperature increase in the sensitive polymer layer to less than 1 degrees C, whereas previous designs with thermally actuated cantilevers showed a temperature increase of up to 19 degrees C. The lower temperature of the sensitive polymer layer on the cantilever directly improves the sensitivity of the sensor system as the extent of analyte physisorption decreases with increasing temperature. The electromagnetic sensor design shows an almost 2 times larger gas sensitivity than the earlier design, which is thermally actuated and read out using p-diffused resistors. The gas sensor is fabricated using an industrial complementary metal oxide semiconductor (CMOS) process and post-CMOS micromachining.     

A complementary-metal-oxide-semiconductor-field-effect-transistor-compatible atomic force microscopy tip fabrication process and integrated atomic force microscopy cantilevers fabricated with this process

A complementary-metal-oxide-semiconductor-field-effect-transistor-compatible process for the fabrication of atomic force microscopy cantilevers with integrated tips has been developed. For the first time, the tips are fabricated after the completion of the regular complementary metal-oxide-semiconductor-field-effect-transistor fabrication process sequence. On-chip circuit components, such as piezoresistive deflection sensors, deflection actuators, and amplifiers, are fabricated on the mirror-polished surface of the wafer, ensuring optimal performance. The tip fabrication process is based on anisotropic silicon etching at low temperature using a tetramethylammonium hydroxide solution. The anisotropic etching process has been optimized to ensure process controllability. Using the described process, complementary-metal-oxide-semiconductor-field-effect-transistor-based cantilevers with piezoresistive deflection sensors and integrated tips have been successfully fabricated. Force-distance curves and scanning images in constant-force mode have been recorded.     

Complementary metal oxide semiconductor cantilever arrays on a single chip: mass-sensitive detection of volatile organic compounds

The sensing behavior of polymer-coated resonant cantilevers for mass-sensitive detection of volatile organic compounds was investigated. Industrial complementary metal oxide semiconductor (CMOS) technology combined with subsequent CMOS-compatible micromachining was used to fabricate a single-chip system comprising the transducers and all necessary driving and signal-conditioning circuitry. An analytical model was developed to describe the mass-sensing mechanism of polymer-coated resonant cantilevers. The model was validated by measurements of various gaseous analytes. As an exemplary application, the quantitative analysis of a binary mixture using an array of four cantilevers is described. Experimental results are given for the concentration prediction of a mixture of n-octane and toluene. Finally, it was established that the limit of detection achieved with cantilever sensors is comparable to that of other acoustic wave-based gas sensors.     

Compact and low power ADCs for a MEMS-based probe storage device

In this paper, we investigate the most appropriate ADC for an array of probe storage devices. Power consumption and area are crucial in this application, since one ADC is associated with each read channel. The read-channel specifications of the probe storage device require an ADC with seven bits of resolution at a rate of 100 kSample/s. Five different ADC architectures have been implemented for the desired specifications: a first- and a second order discrete-time $\Sigma\Delta,$ Σ Δ , a second order continuous-time $\Sigma\Delta$ Σ Δ and a cyclic ADC. The system and circuit design methods of each architecture are presented. The different architectures are compared based on the measurement results of the five fabricated circuits.     

Measuring and Modeling the Power Consumption of Energy-Efficient FPGA Coprocessors for GEMM and FFT

In this paper we analyze the power consumption and energy efficiency of general matrix-matrix multiplication (GEMM) and Fast Fourier Transform (FFT) implemented as streaming applications for an FPGA-based coprocessor card. The power consumption is measured with internal voltage sensors and the power draw is broken down onto the systems components in order to classify the energy consumed by the processor cores, the memory, the I/O links and the FPGA card. We present an abstract model that allows for estimating the power consumption of FPGA accelerators on the system level and validate the model using the measured kernels. The performance and energy consumption is compared against optimized multi-threaded software running on the POWER7 host CPUs. Our experimental results show that the accelerator can improve the energy efficiency by an order of magnitude when the computations can be undertaken in a fixed point format. Using floating point data, the gain in energy-efficiency was measured as up to 30 % for the double precision GEMM accelerator and up to 5 × for a 1k complex FFT.     

Exploring the Design Space of an Energy-Efficient Accelerator for the SKA1-Low Central Signal Processor

The Square Kilometre Array (SKA) will be the biggest radio telescope ever built, with unprecedented sensitivity, angular resolution, and survey speed. Collectively, the SKA’s antennas are expected to gather exabytes of data per second and store one petabyte of data every day, requiring exa operations per second for the processing. This paper focuses on the SKA1-Low, the SKA’s aperture-array instrument consisting of 131,072 antennas that will be built in the first phase of the deployment of the project. In particular, our work explores the design of a custom architecture for the central signal processor (CSP) of the SKA1-Low. The CSP processes digitized samples sent by antennas receiving extra-terrestrial radio-frequency signals between 50 and 350 MHz. We describe the challenges in building the CSP, and present a quantitative study for the implementation of a custom hardware architecture for executing the main CSP algorithms. By taking advantage of emerging 3D-stacked-memory devices and by exploring the design space for a 14-nm implementation, we estimate a power consumption of 9.62 W for processing all channels of a sub-band and an energy efficiency at application level of up to 312 GFLOPS/W for our architecture.