Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Department

Electrical Engineering

First Advisor's Name

Shekhar Bhansali

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Al-Aakhir Rogers

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Irene Calizo

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Sakhrat Khizroev

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

William Kinzy Jones

Fifth Advisor's Committee Title

Committee Member

Sixth Advisor's Name

Subramanian Krishnan

Sixth Advisor's Committee Title

Committee Member

Seventh Advisor's Name

Roberto Panepucci

Seventh Advisor's Committee Title

Committee Member

Keywords

Integrated circuits, security and protection, anti tamper, authentication, electronics packaging, diffraction gratings, subwavelength structures, coupled subwavelength gratings, evanescent waves, wave propagation

Date of Defense

3-27-2015

Abstract

Reliability and sensitive information protection are critical aspects of integrated circuits. A novel technique using near-field evanescent wave coupling from two subwavelength gratings (SWGs), with the input laser source delivered through an optical fiber is presented for tamper evidence of electronic components. The first grating of the pair of coupled subwavelength gratings (CSWGs) was milled directly on the output facet of the silica fiber using focused ion beam (FIB) etching. The second grating was patterned using e-beam lithography and etched into a glass substrate using reactive ion etching (RIE). The slightest intrusion attempt would separate the CSWGs and eliminate near-field coupling between the gratings. Tampering, therefore, would become evident.

Computer simulations guided the design for optimal operation of the security solution. The physical dimensions of the SWGs, i.e. period and thickness, were optimized, for a 650 nm illuminating wavelength. The optimal dimensions resulted in a 560 nm grating period for the first grating etched in the silica optical fiber and 420 nm for the second grating etched in borosilicate glass. The incident light beam had a half-width at half-maximum (HWHM) of at least 7 µm to allow discernible higher transmission orders, and a HWHM of 28 µm for minimum noise. The minimum number of individual grating lines present on the optical fiber facet was identified as 15 lines. Grating rotation due to the cylindrical geometry of the fiber resulted in a rotation of the far-field pattern, corresponding to the rotation angle of moiré fringes. With the goal of later adding authentication to tamper evidence, the concept of CSWGs signature was also modeled by introducing random and planned variations in the glass grating.

The fiber was placed on a stage supported by a nanomanipulator, which permitted three-dimensional displacement while maintaining the fiber tip normal to the surface of the glass substrate. A 650 nm diode laser was fixed to a translation mount that transmitted the light source through the optical fiber, and the output intensity was measured using a silicon photodiode. The evanescent wave coupling output results for the CSWGs were measured and compared to the simulation results.

Identifier

FI15032173

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