Publications – 2010

I. Meric, C. Dean, A. F. Young, J. Hone, P. Kim, and K. L. Shepard, “Graphene field-effect transistors based on boron nitride gate dielectrics,” International Electron Devices Meeting, 2010, pp. 23.2.1-23.2.4.

Graphene field-effect transistors are fabricated utilizing single-crystal hexagonal boron nitride (h-BN), an insulating isomorph of graphene, as the gate dielectric. The devices exhibit mobility values exceeding 10,000 cm2/V-sec and current saturation down to 500 nm channel lengths with intrinsic transconductance values above 400 mS/mm. The work demonstrates the favorable properties of using h-BNas a gate dielectric for graphene FETs.

S. Realov and K. L. Shepard, “Random telegraph noise in 45-nm CMOS: analysis using an on-chip test and measurement system,” International Electron Devices Meeting, 2010, pp. 28.2.1-28.2.4.

RTN measurements in 45-nm CMOS across device bias and geometry using an on-chip characterization system are reported. An automated methodology for extracting RTN levels, amplitude and dwell times is developed. Complex RTN magnitude is statistically modeled, and device size and bias parameter dependencies of the developed model are examined.

R. M. Field, J. Lary, J. Cohn, L. Paninski, and K. L. Shepard, “A low-noise, single-photon avalanche diode in standard 0.13 μm complementary metal-oxide-semiconductor process,” Applied Physcis Letters, 97, 211111 (2010).

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We present the design and characterization of a single-photon avalanche diode SPAD fabricated with a standard 0.13 m complementary metal-oxide-semiconductor process. We have developed a figure of merit for SPADs when these detectors are employed in high frame-rate fluorescent lifetime imaging microscopy, which allows us to specify an optimal bias point for the diode and compare our diode with other published devices. At its optimum bias point at room temperature, our SPAD achieves a photon detection probability of 29% while exhibiting a dark count rate of only 231 Hz and an impulse response of 198 ps.

Z. Jia, I. Meric, K. L. Shepard, and I. Kymissis, “Doping and Illumination Dependence of 1/f Noise in Pentacene Thin-Film Transistors,” IEEE Electron Device Letters, vol.31, no.9, pp.1050-1052, September 2010.

We characterize the influence of interfacial trap sites on carrier scattering and subsequent contribution to channel noise by taking 1/f noise measurements on pentacene organic field effect transistors (OFETs). The noise dependence on drain current from OFETs with UV-ozone treated parylene gate dielectric before the deposition of the semiconductor is compared to that of otherwise identical OFETs with no air exposure during fabrication. Our studies indicate a different noise characteristic in the two samples, which is further confirmed by increasing the carrier density under illumination and comparing the noise spectrum for photogenerated charges with gate-field-induced carriers.

C. R. Dean, A. F. Young, I. Meric, C. Lee, L. Wang, S. Sorgenfrei, K. Watanabe, T. Taniguchi, P. Kim, K. L. Shepard, J. Hone “Boron nitride substrate for high-quality graphene electronics,” Nature Nanotechnology 5, 722-726, 22 August 2010.

Graphene devices on standard SiO2 substrates are highly disordered, exhibiting characteristics that are far inferior to the expected intrinsic properties of graphene1–12. Although suspending the graphene above the substrate leads to a substantial improvement in device quality13,14, this geometry imposes severe limitations on device architecture and functionality. There is a growing need, therefore, to identify dielectrics that allow a substrate-supported geometry while retaining the quality achieved with a suspended sample. Hexagonal boron nitride (h-BN) is an appealing substrate, because it has an atomically smooth surface that is relatively free of dangling bonds and charge traps. It also has a lattice constant similar to that of graphite, and has large optical phonon modes and a large electrical bandgap. Here we report the fabrication and characterization of high-quality exfoliated mono- and bilayer graphene devices on single-crystal h-BN substrates, by using a mechanical transfer process. Graphene devices on h-BN substrates have mobilities and carrier inhomogeneities that are almost an order of magnitude better than devices on SiO2. These devices also show reduced roughness, intrinsic doping and chemical reactivity. The ability to assemble crystalline layered materials in a controlled way permits the fabrication of graphene devices on other promising dielectrics15 and allows for the realization of more complex graphene heterostructures.

Johnston, M. L.; Kymissis, I.; Shepard, K. L., “FBAR-CMOS Oscillator Array for Mass-Sensing Applications,” Sensors Journal, IEEE , vol.10, no.6, pp.1042-1047, June 2010.

Thin-film bulk acoustic resonators (FBAR) are an effective platform for sensitive biological and chemical detection, where their high operating frequencies make them many times more sensitive than a quartz crystal microbalance. Here, we present a monolithic, solidly mounted FBAR oscillator array on CMOS for mass-sensing applications. Through monolithic integration with CMOS drive circuitry, we aim to overcome the spatial and parasitic load limitations of externally coupled resonators to build dense sensor arrays without specialized fabrication techniques. The sensors in this work are constructed in a 6 4 array atop a 0.18μm CMOS active substrate, and mass sensitivity comparable to off-chip FBAR sensors is demonstrated.

C.J. Chen, C.A. Husko, I. Meric, K.L. Shepard, C.W. Wong, W.M. J. Green, Y.A. Vlasov, and S. Assefa, “Deterministic tuning of slow-light in photonic crystal waveguides through the C and L bands by atomic layer deposition,” Applied Physics Letters, 96, 081107 (2010).

We demonstrate digital tuning of the slow-light regime in silicon photonic-crystal waveguides by performing atomic layer deposition of hafnium oxide. The high group-index regime was deterministically controlled redshift of 14010 pm per atomic layer without affecting the group-velocity dispersion and third-order dispersion. Additionally, differential tuning of 11030 pm per monolayer of the slow-light TE-like and TM-like modes was observed. This passive postfabrication process has potential applications including the tuning of chip-scale optical interconnects, as well as Raman and parametric amplification.