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.
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.
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.
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
ITT Geospatial Systems has space-qualified a visible band interline Charge Coupled Device (CCD) image
sensor with 18 million pixels developed using commercial technology. The sensor is comprised of an 4320
(H) x 4144 (V) array of 8 micron square pixels. With multiple analog outputs each operating at 20 MHz
the sensor will support 30 frames per second continuous video capture. The pixel incorporates a pinned
photodiode, vertical overflow drain and microlens to achieve low dark current, lag-free imaging with highspeed
global electronic shutter at high quantum efficiency (QE). The vertical and horizontal CCD's are
true two-phase designs which support an integrate-while-read operation. The sensor chip is mounted on an
Aluminum Nitride co-fired ceramic package optimized for electrical signal integrity, thermal and optical
stability. The architecture supports quadrant redundancy. The complete assembly has been space-qualified
to a Technology Readiness Level (TRL) of 6 with Total Ionization Dose (TID) radiation testing at 25 Krad.
The sensor exceeds 12-bit of dynamic range and 31% QE with 5 W of total power. The nonlinearity is
measured to be 1.0% while the global non-uniformity is less than 2%. The low defect density of the CCD
sensor allows high resolution video imaging in a space environment.