Erli Chen

Fabrication of 10 nm enclosed nanofluidic channels

We made uniform arrays of nanometer scale structures using nanoimprint lithography over large areas (100 mm wafers). The nanofluidic channels were further narrowed and sealed by techniques that are based on nonuniform deposition. The resulting sealed channels have a cross section as small as 10 nm by 50 nm, of great importance for confining biological molecules into ultrasmall spaces. These techniques can be valuable fabrication tools for Nanoelectromechanical Systems and Micro/Nano Total Analysis Systems.

Characteristics of coplanar transmission lines on multilayer substrates: modeling and experiments

Characteristics of coplanar transmission lines on multilayer substrates expressed in analytic formulas have been obtained using conformal mapping. The accuracy of these formulas has been verified experimentally on a variety of coplanar transmission lines using differential electro-optic (DEOS) sampling. For coplanar waveguides, the theory differs from the experiment by less than 3%; for coplanar striplines, the differences are less than 6%.

140‐GHz metal‐semiconductor‐metal photodetectors on silicon‐on‐insulator substrate with a scaled active layer

Metal‐semiconductor‐metal photodetectors with 100‐nm finger spacing and width on a silicon‐on‐insulator substrate that has a scaled active layer were fabricated and characterized using electro‐optic sampling. The unique device structure cuts off carriers generated deep inside the semiconductor substrate, resulting in a measured response time of 3.2 ps and a bandwidth of 140 GHz. Furthermore, the detector structure makes the detector’s speed independent of the light penetration depth and thus the light wavelength. Good metal‐semiconductor Schottky contact and low detector dark current have been achieved.

10 nm Si pillars fabricated using electron‐beam lithography, reactive ion etching, and HF etching

This article reports the fabrication and preliminary photoluminescence (PL) study of free‐standing Si pillars with diameters of about 10 nm and aspect ratios greater than 15. The pillars were fabricated using electron‐beam lithography, chlorine based reactive ion etching (RIE), and subsequent HF wet etching. Using HF etching offers several advantages: (a) it is a relatively stress independent process and therefore preserves the original shape of the structure; (b) it is a room temperature process; (c) it has a very controllable etch rate, ∼1.9 nm/h; and (d) it can remove RIE damage and passivate the Si surface. PL with a peak at 720 nm was repeatedly observed from an array of nanoscale pillars with ∼20 nm diameters. However, the cause of such PL is still unclear.

High-efficiency and high-speed silicon metal–semiconductor–metal photodetectors operating in the infrared

A silicon metal–semiconductor–metal photodetector with high-efficiency and high-speed in the infrared is reported. The high performance is achieved by using a Si-on-insulator substrate with a patterned nanometer-scale scattering reflector buried underneath a 170-nm-thick Si active layer. This scattering reflector causes light to be trapped inside the thin Si active layer, resulting in a fast and efficient carrier-collection by the electrodes. The impulse response of the photodetector, measured by electro-optic sampling at 780 nm wavelength, has a full width at half-maximum of 5.4 ps, corresponding to a 3-dB bandwidth of 82 GHz. At both 633 and 850 nm wavelengths, the responsivities of the photodetector with the buried backside reflector are at least an order of magnitude larger than those without the reflector.

Polarimetry of thin metal transmission gratings in the resonance region and its impact on the response of metal-semiconductor-metal photodetectors

The resonance behavior of metal transmission gratings and its impact on the response of metal-semiconductor-metal (MSM) photodetectors have been studied experimentally and theoretically. The metal gratings, with finger spacings in the subwavelength region of the visible light, were fabricated using e-beam lithography and lift-off. Strong resonances have been observed only in the S polarization. As a result, the light transmitted through a grating is primarily S polarized if the grating’s finger spacing is less than one-third of the wavelength of the incident light, but P polarized otherwise. Similar phenomenon has been observed in the response of MSM photodetectors since the fingers (electrodes) of an MSM photodetector basically form a grating. Theoretical simulations employing the rigorous modal-expansion theory fairly predict the observed phenomenon.

Group velocities in coplanar strip transmission lines on Si and Si/SiO2/Si substrates measured using differential electro‐optic sampling

The group velocities in coplanar strip transmission lines on Si and Si/SiO2/Si substrates were compared experimentally and theoretically. To ensure the experimental accuracy, a differential electro‐optic sampling system with a delay‐time resolution of 30 fs and a spatial resolution of 1 μm has been developed. Compared with the group velocity on a Si substrate, the group velocity on a Si/SiO2/Si substrate with a 2.2 μm SiO2 layer was found to be 10% faster, which agrees well with the theoretical prediction.

High-efficiency and high-speed metal-semiconductor-metal photodetectors on Si-on-insulator substrates with buried backside reflectors

We report Si metal-semiconductor-metal photodetectors with high-efficiency and high-speed in the infrared using Si-on- insulator substrates with backside reflectors buried underneath a deep-submicron-thick active layer. The reflectors cause the trapping of the light inside the thin Si active layer, resulting in a fast and efficient carrier- collection by the electrodes. The impulse response of the photodetector, measured by electro-optic sampling at 780 nm wavelength, has a full width at half-maximum of 5.4 ps, corresponding to a 3-dB bandwidth of 82 GHz. At both 633 and 850 nm wavelengths, the responsivities of the photodetectors with the buried backside reflectors are at least an order of magnitude larger than that of those without the reflectors.

Fabrication of high-performance MSM photodetectors on SOI with nanometer-scale scattering buried backside reflectors

We present the fabrication and performance of a metal- semiconductor -metal (MSM) photodetector with high efficiency and high speed. The MSM photodetector is fabricated on a SOI substrate with a 170-nm-thick Si active layer. A scattering backside reflector, consisting of inverted pyramids with 193- nm-long sides and 54.7 degree slopes, is buried underneath the active layer. This scattering buried backside reflector (SBBR) causes the trapping of light inside the active layer, resulting in an MSM photodetector with a response time of 5.4 ps and responsivity comparable with those on bulk Si at both the visible and infrared.