Francisco Tejada

A low-power 8-bit SAR ADC for a QCIF image sensor

In this paper, we report on an 8-bit auto-calibrating successive-approximation-register (SAR) analog-to-digital converter (ADC) for ultra-low power image sensors. The fabricated design includes an on-chip bandgap voltage reference and a tunable clock generator in addition to the SAR ADC core circuitry. Aside from two power pins, the design uses only one extra pin to output the digitized samples serially. Power consumption for the design is 21µW at 0.8V supply voltage, and it is 32µW including ancillary circuits. The sampling rate varies from 370kS/s to 1.6MS/s depending on the supply voltage. The design occupies an area of 0.2mm2 in a 0.18µm CMOS process, of which 0.073mm2 is for the SAR ADC core.

A CMOS Neural Interface for a Multichannel Vestibular Prosthesis

We present a high-voltage CMOS neural-interface chip for a multichannel vestibular prosthesis (MVP) that measures head motion and modulates vestibular nerve activity to restore vision- and posture-stabilizing reflexes. This application specific integrated circuit neural interface (ASIC-NI) chip was designed to work with a commercially available microcontroller, which controls the ASIC-NI via a fast parallel interface to deliver biphasic stimulation pulses with 9-bit programmable current amplitude via 16 stimulation channels. The chip was fabricated in the ONSemi C5 0.5 micron, high-voltage CMOS process and can accommodate compliance voltages up to 12 V, stimulating vestibular nerve branches using biphasic current pulses up to 1.45±0.06 mA with durations as short as 10 μs/phase. The ASIC-NI includes a dedicated digital-to-analog converter for each channel, enabling it to perform complex multipolar stimulation. The ASIC-NI replaces discrete components that cover nearly half of the 2nd generation MVP (MVP2) printed circuit board, reducing the MVP system size by 48% and power consumption by 17%. Physiological tests of the ASIC-based MVP system (MVP2A) in a rhesus monkey produced reflexive eye movement responses to prosthetic stimulation similar to those observed when using the MVP2. Sinusoidal modulation of stimulus pulse rate from 68-130 pulses per second at frequencies from 0.1 to 5 Hz elicited appropriately-directed slow phase eye velocities ranging in amplitude from 1.9-16.7 °/s for the MVP2 and 2.0-14.2 °/s for the MVP2A. The eye velocities evoked by MVP2 and MVP2A showed no significant difference (t-test, p=0.34), suggesting that the MVP2A achieves performance at least as good as the larger MVP2.

Stacked, standing wave detectors in 3D SOI-CMOS

We report on the design of stacked standing wave detectors in a 3D SOI CMOS technology. The standing wave detector is the basic block needed to implement a die level CMOS interferometer to measure small displacements. The 3D CMOS process allows for standing wave detectors to be vertically stacked which provides directional information as well as displacement information from the interferometer. We discuss design considerations for the photodiodes and MOS amplifier

An SOS MEMS interferometer

The function of a large number of MEMS and NEMS devices relies critically on the transduction method employed to convert the mechanical displacement into electrical signal. Optical transduction techniques have distinct advantages over more traditional capacitive and piezoelectric transduction methods. Optical interferometers can provide a much higher sensitivity, about 3 orders of magnitude, but are hardly compatible with standard MEMS and microelectronics processing. In this paper, we present a scalable architecture based in silicon on sapphire (SOS) CMOS 1 for building an interferometric optical detection system. This new detection system is currently being applied to the sense the motion of a resonating MEMS device, but can be used to detect the motion of any object to which the system is packaged. In the current hybrid approach the SOS CMOS device is packaged with both vertical cavity surface emitting lasers (VCSELs) and MEMS devices. The optical transparency of the sapphire substrate together with the ultra thin silicon PIN photodiodes available in this SOS process allows for the design of both a Michelson type and Fabry Perot type interferometer. The detectors, signal processing electronics and VCSEL drivers are built on the SOS CMOS for a complete system. We present experimental data demonstrating interferometric detection of a vibrating device.

Surface micromachining in Silicon on Sapphire CMOS technology

We report on the design and fabrication of surface micromachined microelectromechanical structures (MEMS) in an ultra thin silicon (UTSi) on sapphire CMOS process [Peregrine Semiconductor (PE) Silicon on Sapphire (SOS) process]. This is the first demonstration of surface micromachined MEMS structures in a CMOS process fabricated on a sapphire substrate.

Silicon on sapphire CMOS architectures for interferometric array readout

The performance of microelectromechanical sensor systems relies critically on the transduction method employed to convert the mechanical displacement into an electrical signal. Optical readout techniques have distinct advantages over more traditional capacitive and piezoelectricity transduction methods. They are employed in applications where atomic resolution with a small sensing area is necessary, for example, scanning probe microscopes. In this paper, we present two architectures for optoelectronic sensing based on silicon on sapphire CMOS (SOS-CMOS) technology. We show how to heterogeneously integrate photodetectors, analog CMOS signal processing circuits, and VCSELs for an array based optical readout system. The optical transparency of the sapphire substrate allows for the design of both Michelson and Fabry-Perot type interferometers that are amenable to 2D array sensing. We present preliminary experimental data demonstrating standing wave detection in the 100 nm thin silicon PIN photodiodes available in the SOS-CMOS technology for the Fabry-Perot interferometer.

Miniature atomic scalar magnetometer for space based on the rubidium isotope 87Rb

Abstract A miniature atomic scalar magnetometer based on the rubidium isotope 87Rb was developed for operation in space. The instrument design implements both Mx and Mz mode operation and leverages a novel microelectromechanical system (MEMS) fabricated vapor cell and a custom silicon‐on‐sapphire (SOS) complementary metal‐oxide‐semiconductor (CMOS) integrated circuit. The vapor cell has a volume of only 1 mm3 so that it can be efficiently heated to its operating temperature by a specially designed, low‐magnetic‐field‐generating resistive heater implemented in multiple metal layers of the transparent sapphire substrate of the SOS‐CMOS chips. The SOS‐CMOS chip also hosts the Helmholtz coil and associated circuitry to stimulate the magnetically sensitive atomic resonance and temperature sensors. The prototype instrument has a total mass of fewer than 500 g and uses less than 1 W of power, while maintaining a sensitivity of 15 pT/√Hz at 1 Hz, comparable to present state‐of‐the‐art absolute magnetometers.

Characterization of RTN noise in the analog front-end of digital pixel imagers

The interest for more digital functionality in the readout circuits for imagers is growing rapidly. Similarly, there are advantages to having the pixel pitch smaller from visible to long wave IR. The front end is the dominant source of electronic noise for an in-pixel digital design. Limiting the real estate considerably would force the design to smaller feature size, which may worsen the random telegraph signal or noise (RTS/RTN) that will likely be the dominate source for noise for these imagers. This paper summarizes initial results for RTN sensitivities at room temperature to various device types, geometries, and flux rates, evaluated on a digital pixel on 65- and 55-nm CMOS processes.

Large scale micro-Fabry-Perot optical filter arrays

Fabry-Perot filter arrays have been fabricated comprised of six million individual filters using standard semiconductor processing techniques. The current 3000x2000 array consists of 5x5 sub-arrays in which each of the nine micron wide Fabry-Perot filters in the sub-array has a different color response. The 5x5 sub-array is replicated to create a 600x400 matrix of 5x5 micro Fabry-Perot filter sub-arrays. This Fabry-Perot matrix has been integrated with a commercially available panchromatic 6 Megapixel CCD focal plane array to create a 25 color hyperspectral camera with 600x400 imaging pixels. Near-UV, visible and NIR filter arrays have been fabricated. The semiconductor processing technique permits filter arrays of general filter size, shape, configuration and distribution to be implemented with ease.

An interference microfilter array with tunable spectral response for each pixel

A standing wave spectrometer is turned into a wavelength tunable band-pass filter by the addition of a reflective coating. It results in the standing wave filter (SWF), a miniaturized Fabry-Perot band-pass filter with a semi-transparent detector that can be constructed into a pixel-tunable focal plane array, suitable for hyperspectral imaging applications. The asymmetric Fabry-Perot cavity is formed between the reflective coating and a tunable mirror, originally part of the spectrometer. The predicted performance of the SWF is optimized through modeling based on the matrix formalism used in thin film optics and with FDTD simulations. The SWF concept is taken from an ideal device to a focal plane array design that was fabricated with 40 micron pixels using semi-conductor processing technology. First-light spectra measured from the 100 pixel Standing Wave Filter array agree with predictions and prove the concept.