Passive Millimeter Wave Imaging for Homeland Security and Safety via Si-based Backward Diode Sensors, Paul R. Berger

Advisor: Paul R. Berger Students: Si-Young Park (ECE Ph.D. candidate) Ms. Anisha Ramesh (ECE Ph.D. candidate) Dan Twaddell (Undergraduate Researcher) Collaborators: Phillip E. Thompson (Naval Research Laboratory) Patrick J. Fay (University of Notre Dame) Charles L. A. Cerny (AFRL-WPAFB) Joseph E. Van Nostrand, (AFRL-WPAFB) Former Graduate Students: Sung-Yong Chung (Ph.D. 2005) Niu Jin (Ph.D. 2004)

Importance of the Problem:

This project demonstrates Si-based sensors with high room temperature curvature coefficient which is suitable for seamless integration with Si readout circuitry for passive millimeter-wave detection of reflected RF energy for detection of concealed weapons and pilot assistance through rain, fog and smoke. Highest reported zero-bias curvature coefficient of any Si-based backward diode (2-fold increase). A high nonlinearity directly correlates to high sensitivity for a passive millimeter-wave camera system suitable for detection of concealed weapons and vision through fog, smoke and other obscuring media for transportation safety.

Brief Description of Our Work and Results:

High sensitivity Si-based backward diodes were realized that are monolithically integratable with transistor circuitry. Potential applications include large area focal plane arrays. The Si-based backward diodes exhibit a high zero-biased curvature coefficient, g, of 31 V^-1 and a low zero biased junction capacitance, C_j, of 9 fF/m², all at room temperature. The predicted low frequency voltage sensitivity, b_v, for a 50 W source is 3100 V/W. The high sensitivity, low junction capacitance, and Si/SiGe heterojunction bipolar transistor (HBT) compatibility of the Si-based backward diodes make them very attractive for zero-bias square-law detector applications.

Silicon-based backward diodes incorporating delta-doped active regions for direct detection of microwave radiation with zero external dc bias was demonstrated at room temperature and sensitivity characterized. The resulting backward diodes, which were grown by low temperature molecular beam epitaxy, show a high zero-bias curvature coefficient ( ) of 23.2 V-1 with a junction resistance (Rj) of 687 kohm for a 5 micron diameter diode. The microwave-frequency voltage sensitivity is reported for the first time; a measured sensitivity of 2376 V/W is obtained at zero-bias. An intrinsic 3-dB cutoff frequency of 1.8 GHz was determined based on an extracted series resistance of 290 ohm and a junction capacitance of 0.307 pF using a small signal model established to fit the measured S-parameters.

Patents

• "Silicon-based Backward Diodes for Zero-biased Square Law Detection and Detector Arrays of Same," Paul R. Berger, Niu Jin, and Phillip E. Thompson, [Disclosure submitted on July 7, 2004; provisional filed April 19, 2005, full patent filed April 19, 2006, Serial. No. & Code 60/672,833 and 11/407,120].

Publications

1. "Sensitivity of Si-Based Zero-Bias Backward Diodes for Microwave Detection," Si-Young Park, Ronghua Yu, Sung-Yong Chung, Paul R. Berger, Phillip E. Thompson, and Patrick Fay, Electronics Letters, 43, pp. 53-54 (March 1, 2007). PDF (118 kB)

2. "High Sensitivity Si-Based Backward Diodes for Zero-Biased Square-Law Detection and the Effect of Post-Growth Annealing on Performance," Niu Jin, Ronghua Yu, Sung-Yong Chung, Paul R. Berger, Phillip E. Thompson, and Patrick Fay, IEEE Electron Device Letters, 26, pp. 575-578 (August 2005). PDF (117 kB)

Invited Talks

1. "Si-based Tunnel Junction Devices for Sub-Terahertz Communication and Imaging," Paul R. Berger and Phillip E. Thompson , SPIE's Optics East 2006: Terahertz Physics, Devices, and Systems, Boston, MA (December 2-4, 2006). SPIE Terahertz Conference website

Conference Presentations

2. "Delta-Doped Si/SiGe Zero-Bias Backward Diodes for Micro-Wave Detection," Si-Young Park, Ronghua Yu, Sung-Yong Chung, Paul R. Berger, Phillip E. Thompson and Patrick Fay, Device Research Conference at Notre Dame University (June 2007).

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