Rochester Institute of Technology (RIT) and its collaborators at the University of Rochester and Harris Corporation are developing a room-temperature imaging Terahertz (THz) frequency detector using Si-MOSFET (Silicon Metal Oxide Semiconductor Field Effect Transistor) CMOS devices. They are implemented into a focal plane imaging array for use in many applications, such as transmission or penetration imaging and spectroscopy. Technology for THz detection is often extremely costly, due to either expensive detector materials or cryogenic cooling systems. However, the devices tested here are low-cost due to the use of conventional room temperature silicon CMOS technology. The devices operate from 170 to 250 GHz with an additional detector design has been fabricated for 30 THz (10 microns wavelength). Results are presented for the initial testing of single test structure FETs. These devices were designed with several different antenna configurations and a range of MOSFET design variations for evaluation. The primary goal of the work presented here is to determine the optimized detector design for the subsequent focal plane array implementation based on the largest responsivities and lowest noise-equivalent power (NEP). Transmission testing of the devices yields responsivities of about 100 to 1000 V/W and a NEP of about 0.5 to 10 nW·Hz-1/2. Through this evaluation and by utilizing signal amplification on the chip, signal modulation at higher frequencies, and smaller process sizes the performance of these devices will continue to improve in future designs.
Exelis Geospatial Systems and its CEIS partners at the University of Rochester and Rochester Institute of Technology are developing an active THz imaging system for use in standoff detection, molecular spectroscopy and penetration imaging. The current activity is focused on developing a precision instrument for the detection of radiation centered on atmospheric windows between 200 GHz and 400 GHz (available sources). A transmission imager is developed by raster scanning through a semi-coherent non-ionizing beam, where the beam is incident on a NMOS FET detector. The primary goal of the initial system is to produce a setup capable of measuring responsivity and sensitivity of the detector. The Instrumentation covers the electromagnetic spectral range between 188 GHz and 7.0 THz. Transmission measurements are collected at 188 GHz in order to verify image formation, responsivity and sensitivity as well as demonstrate the active imager’s ability to make penetration images.
Collaboration between Exelis Geospatial Systems with University of Rochester and Rochester Institute of Technology aims to develop an active THz imaging focal plane array utilizing 0.35um CMOS MOSFET technique. An appropriate antenna is needed to couple incident THz radiation to the detector which is much smaller than the wavelength of interest. This paper simply summarizes our work on modeling the optical characteristics of bowtie antennae to optimize the design for detection of radiation centered on the atmospheric window at 215GHz. The simulations make use of the finite difference time domain method, calculating the transmission/absorption responses of the antenna-coupled detector.
Interest in array based imaging of terahertz energy (T-Rays) has gained traction lately, specifically using a CMOS process due to its ease of manufacturability and the use of MOSFETs as a detection mechanism. Incident terahertz radiation on to the gate channel region of a MOSFET can be related to plasmonic response waves which change the electron density and potential across the channel. The 0.35 μm silicon CMOS MOSFETs tested in this work contain varying structures, providing a range of detectors to analyze. Included are individual test transistors for which various operating parameters and modes are studied and results presented. A focus on single transistor-antenna testing provides a path for discovering the most efficient combination for coupling 0.2 THz band energy. An evaluation of fabricated terahertz band test detection MOSFETs is conducted. Sensitivity analysis and responsivity are described, in parallel with theoretical expectations of the plasmonic response in room temperature conditions. A maximum responsivity of 40 000 V/W and corresponding NEP of 10 pW/Hz1/2 (±10% uncertainty) is achieved.
Exelis Geospatial Systems and its CEIS partners at the University of Rochester and Rochester Institute of Technology
are developing an active THz imaging focal plane for use in standoff detection, molecular spectroscopy and penetration
imaging. This activity is focused on the detection of radiation centered on the atmospheric window at 215.5 GHz. The
pixel consists of a direct coupled bowtie antenna utilizing a 0.35 μm CMOS technology MOSFET, where the plasmonic
effect is the principle method of detection. With an active THz illumination source such as a Gunn diode, a design of
catadioptric optical system is presented to achieve a resolution of 3.0 mm at a standoff distance of 1.0 m. The primary
value of the initial system development is to predict the optical performance of a THz focal plane for active imaging and
to study the interaction of THz radiation with various materials.
We describe preliminary design, modeling and test results for the development of a monolithic, high pixel density,
THz band focal plane array (FPA) fabricated in a commercial CMOS process. Each pixel unit cell contains multiple
individual THz band antennae that are coupled to independent amplifiers. The amplified signals are summed either
coherently or incoherently to improve detection (SNR). The sensor is designed to operate at room temperature using
passive or active illumination. In addition to the THz detector, a secondary array of Visible or SWIR context
imaging pixels are interposed in the same area matrix. Multiple VIS/SWIR context pixels can be fabricated within
the THz pixel unit cell. This provides simultaneous, registered context imagery and "Pan sharpening" MTF
enhancement for the THz image. The compact THz imaging system maximizes the utility of a ~ 300 μm x 300 μm
pixel area associated with the optical resolution spot size for a THz imaging system operating at a nominal ~ 1.0
THz spectral frequency. RF modeling is used to parameterize the antenna array design for optimal response at the
THz frequencies of interest. The quarter-wave strip balanced bow-tie antennae are optimized based on the
semiconductor fabrication technology thin-film characteristics and the CMOS detector input impedance. RF SPICE
models enhanced for THz frequencies are used to evaluate the predicted CMOS detector performance and optimal
unit cell design architecture. The models are validated through testing of existing CMOS ROICs with calibrated THz
Unattended ground monitoring that combines seismic and acoustic information can be a highly valuable tool in
intelligence gathering; however there are several prerequisites for this approach to be viable. The first is high
sensitivity as well as the ability to discriminate real threats from noise and other spurious signals. By combining
ground sensing with acoustic and image monitoring this requirement may be achieved. Moreover, the DS Sentry®provides innate spurious signal rejection by the "active-filtering" technique employed as well as embedding some
basic statistical analysis. Another primary requirement is spatial and temporal coverage. The ideal is
uninterrupted, long-term monitoring of an area. Therefore, sensors should be densely deployed and consume very
little power. Furthermore, sensors must be inexpensive and easily deployed to allow dense placements in critical
areas. The ADVIS DS Sentry®, which is a fully-custom integrated circuit that enables smart, micro-power
monitoring of dynamic signals, is the foundation of the proposed system. The core premise behind this technology
is the use of an ultra-low power front-end for active monitoring of dynamic signals in conjunction with a highresolution,
Σ Δ-based analog-to-digital converter, which utilizes a novel noise rejection technique and is only
employed when a potential threat has been detected. The DS Sentry® can be integrated with seismic accelerometers
and microphones and user-programmed to continuously monitor for signals with specific signatures such as impacts,
footsteps, excavation noise, vehicle-induced ground vibrations, or speech, while consuming only microwatts of
power. This will enable up to several years of continuous monitoring on a single small battery while concurrently
mitigating false threats.
We describe a CMOS image sensor with column-parallel delta-sigma (ΔΣ) analog-to-digital converter (ADC). The
design employs three transistor pixels (3T1) where the unique configuration of the ΔΣ ADC reduces the noise
contribution of the readout transistor. A 128 x 128 pixel image sensor prototype is fabricated in 0.35μm TSMC
technology. The reset noise and the offset fixed pattern noise (FPN) are removed in the digital domain. The
measured readout noise is 37.8μV for an exposure time of 33ms. The low readout noise allows an improved low
light response in comparison to other state-of-art designs. The design is suitable for applications demanding
excellent low-light response such as astronomical imaging. The sensor has a measured intra-scene dynamic range
(DR) of 91 dB, and a peak signal-to-noise ratio (SNR) of 54 dB.
This paper is a progress report of the design and characterization of a monolithic CMOS detector with an on-chip ΣΔ
ADC. A brief description of the design and operation is given. Backside processing steps to allow for backside
illumination are summarized. Current characterization results are given for pre- and post-thinned detectors.
Characterization results include measurements of: gain photodiode capacitance, dark current, linearity, well depth,
relative quantum efficiency, and read noise. Lastly, a detector re-design is described; and initial measurements of its
photodiode capacitance and read noise are presented.
The Rochester Imaging Detector Laboratory, University of Rochester, Infotonics Technology Center, and Jet Process
Corporation developed a hybrid silicon detector with an on-chip sigma-delta (ΣΔ) ADC. This paper describes the process
and reports the results of developing a fabrication process to robustly produce high-quality bump bonds to hybridize a
back-illuminated detector with its ΣΔ ADC. The design utilizes aluminum pads on both the readout circuit and the
photodiode array with interconnecting indium bumps between them. The development of the bump bonding process is
discussed, including specific material choices, interim process structures, and final functionality. Results include
measurements of bond integrity, cross-wafer uniformity of indium bumps, and effects of process parameters on the final
product. Future plans for improving the bump bonding process are summarized.