Hiroaki Honma

Continuous control of surface-plasmon excitation wavelengths using nanomechanically stretched subwavelength grating

We report a new method for continuously controlling surface-plasmon (SP) excitation wavelengths using a nanomechanically stretched metal subwavelength grating. An aluminum subwavelength grating is integrated with electrostatic comb-drive actuators to expand the metal subwavelength period, which allows continuous control of the dependent excitation wavelength. We successfully demonstrated that the excitation wavelength over the 542–668 nm range varies continuously with the square of the applied voltage, which agrees well with the theory of electrostatic actuation. This new modulation method can provide the functions of readjustment and continuous tuning for SP-based devices.

A Low-Voltage and High Uniformity Nano-Electro-Mechanical System Tunable Color Filter Based on Subwavelength Grating

This paper reports on the construction of a nano-electro-mechanical system (NEMS) tunable color filter based on a subwavelength grating with high color uniformity and a low drive voltage. We recently proposed a ground-voltage-ground (GVG)-type tunable color filter with a parallel-plate actuator with three pairs of electrodes to decrease the crosstalk due to the electrostatic attractive force between each pair of actuators. Our finite element method (FEM) simulation results indicate that the drive voltage is decreased by 10 V, as compared to that of the previously reported GV type. The proposed structure was fabricated using a silicon-on-insulator (SOI) wafer. The color tuning capability of the device was demonstrated by applying a drive voltage of 6.7 V. The reflected light intensity was decreased by 34% at a wavelength of 680 nm. Color uniformity was also obtained in the filter area by reducing the variation of the displacement on the one-dimensional actuator arrays.

Monolithic integration of NEMS tunable color filter and LSI driver circuits

This paper presents a NEMS (Nano Electro Mechanical System) tunable color filter integrated with MOS driver circuits on an SOI (Silicon on Insulator) wafer. The NEMS electrostatic actuator could be designed a high mechanical resonance frequency with a relatively low drive voltage. The sub-wavelength grating and MOS driver circuits were made in a top and a substrate layer of the SOI wafer, respectively. The tiny anchors and pre-fabricated MOS transistors were covered by parylene N during the sacrificial release process using buffered hydrofluoric acid. Various structural colors depended on the pitch of the sub-wavelength grating were observed from integrated NEMS-LSI chip and NEMS TEG area. The color tuning from yellow to green was demonstrated at 20 V operation.

A tunable plasmonic color filter by nanomechanical stretch using MEMS electrostatic actuator

This paper reports an evaluation of electromechanical properties of the tunable plasmonic color filter by means of a nanomechanical in-plane motion of free-standing Al subwavelength grating. The maximum 707 nm pitch expansion was obtained at an applied voltage of 60 V, which provides a continuous peak shift of transmitted light. The frequency response was achieved up to 1 kHz.

Fabrication of free-standing subwavelength metal–insulator–metal gratings using high-aspect-ratio nanoimprint techniques

In this paper, we report on the construction of a free-standing metal–insulator–metal (MIM) subwavelength grating by nanoimprint and lift-off techniques, which can be used as a plasmonic color filter for imaging a multicolor spectrum. The free-standing subwavelength grating was designed to be composed of Al (50 nm)–SiO2 (150 nm)–Al (50 nm) layers, and the thickness of the SiO2 layer determined the wavelength selectivity for the color filter. The residual-free nanoimprint with an aspect ratio of was applied in the lift-off process to the formation of MIM gratings. We successfully developed subwavelength MIM gratings with heights of more than 200 nm. We also demonstrated the fabrication of a free-standing MIM grating without lateral stiction, which was expected to improve the wavelength selectivity of a free-standing plasmonic color filter.

Surface-plasmon-based flexible color filter using Al nanostructure array on parylene-N thin film

In this study, we propose a flexible color filter based on surface plasmon using aluminum nanowire and nanodot array. Aluminum subwavelength lattice was formed on a parylene-N film and coated with parylene-N to avoid detachment from the substrate film. Both Al nanowire width of 250 nm and nanodot of 250 nm were successfully fabricated on the thin parylene-N film of 200 nm. Green color from the Al nanowire period of 450 nm was demonstrated.

Investigation of filter size and duty ratio on transmission color filter based on surface plasmons

In this paper, we discuss a minimum filter size and duty ratio (= width/period) of a subwavelength Al grating for a tunable RGB color filter based on surface plasmons. An array of Al gratings was deployed over a through hole by sacrificial release process. The peak wavelength of the transmitted light was red-shifted by increasing the period of the subwavelength grating from 450 nm to 600 nm. We obtained enough transmission light intensity from the 10 μm square pixel-size including 20 Al nanowires. The noise-level was found to be dependent on the duty ratio and decreased with increase of the duty ratio.

A 3.3 V operated variable transmission attenuator based on subwavelength grating

This paper presents a nanoelectromechanical system (NEMS) variable transmission attenuator based on a gap variable subwavelength grating with a low drive voltage. An array of parallel-plate actuators is deployed over a through hole. The transmitted light intensity decreased from 63.3% to 46.5% with a drive voltage of 3.2 V at a wavelength of 775 nm.