Deterministic Assembly of Functional Nanodevices onto Silicon Circuits

Open Access
Kim, Jaekyun
Graduate Program:
Electrical Engineering
Doctor of Philosophy
Document Type:
Date of Defense:
January 14, 2010
Committee Members:
  • Theresa Stellwag Mayer, Dissertation Advisor
  • Theresa Stellwag Mayer, Committee Chair
  • Thomas E Mallouk, Committee Member
  • Craig Grimes, Committee Member
  • Jerzy Ruzyllo, Committee Member
  • Nanotechnology
  • Nanowire
Bottom-up integration of nanostructures offers a promising method to achieve material diversity for chemical and biological applications, often considered unattainable by conventional top-down fabrication. Thus, deterministic integration of nanostructures such as nanowires and nanoshell spheres on silicon CMOS circuitry represents a significant step toward cross-reactive silicon CMOS chip where different types of off-chip synthesized sensory materials are merged. Applying this deterministic bottom-up integration to substrate or circuit eliminates the constraints of thermal budget, chemical compatibility, lattice mismatch between nanostructures to be assembled and substrate. This thesis discusses a deterministic assembly strategy for nanowires and spheres and their integrations onto silicon CMOS circuitry for electronic microsystem applications. The nanowire assembly structure was designed to create a dielectrophoretic attractive force toward the electrode gap, resulting in uniformly-spaced rhodium nanowire array due to mutual electrostatic interaction between assembled nanowires. Systematic investigation reagarding nanowire array formation reveals that stronger long-range dielectrophoretic forces attract more nanowires at the electrode gap, forming less-spaced array while stronger electrostatic nanowire interaction results in the larger spacing within the array. Thus, their interplay tends to determine the average spacing between the assembled nanowires. Based on understanding the electrostatistic interaction between assembled nanowires, lithographically defined wells with a localized electric field determines the final alignment position of assembled rhodium nanowires on a substrate. Post-assembly process using electrodeposition and subsequent lift-off process completes monolithic integration of rhodium nanowires while preserving nanowires assembled only within the recessed region. Individual rhodium nanowire assembly yields exceeding 95% were obtained at nanowire densities >105 /cm2 with a submicron registration accuracy. PEDOT/ClO4 nanowire chemical sensors are also fabricated to demonstrate functional nanowire integration for on-chip sensing. This thesis also describes a bottom-up strategy for fabricating ultra-high-density cross-point sensor arrays (>107 elements/cm2) that uses fluidic assembly to position the functional nanoshell microspheres between lithographically-defined electrodes on-chip. Cross-point array structure is designed to accommodate single spherical particles at each cross-point and make them electrically connected to upper and lower access electrodes. As proof-of-concept, PEDOT nanoshell microspheres are assembled to fabricate chemical sensor devices for on-chip application. Individually addressing each PEDOT nanoshell sphere enables monitoring of an array of sphere for conductance change by chemical gas, solvent, humidity. Due to upper and lower electrodes format and intrinsic form factor of spheres, it is advantageous to achieve high integration density compared to nanowires with a high aspect ratio. Additionally, this architectural framework combines the advantages of large surface-to-volume ratio particle-based sensor elements with high sensor redundancy to enhance performance metrics such as detection sensitivity and signal-to-noise ratio.