Spectrometer-based wavelength interrogation SPR imaging via Hadamard transform.

We present spectrometer-based wavelength interrogation surface plasmon resonance imaging (SPRi) without mechanical scanning. A polarized broadband light source illuminates an object via a gold-coated prism; the reflected light is spatially modulated by a digital mirror device (DMD) and then measured with a spectrometer. Reflectance spectral images are reconstructed via the Hadamard transform (HT), and a refractive index (RI) map is visualized from the reflectance spectral images by analyzing the resonance peak shift of the spectrum at each image pixel. We demonstrate the feasibility of our method by evaluating the resolution, sensitivity, and dynamic detection range, experimentally obtained as ∼2.203 × 10-6 RI unit (RIU), ∼3,407 nm/RIU, and ∼0.1403 RIU, respectively. Furthermore, simulations are performed to validate the experimental results.

PLC-Based Integrated Refractive Index Sensor Probe with Partially Exposed Waveguide.

This paper proposes a simple, high-efficiency refractive index (RI) sensor, with a structure based on the planar lightwave circuit (PLC) probe type. The optical sensor has a 1 × 2 splitter structure with reference and sensing channels, each consisting of a U-shaped waveguide structure that is configured by connecting C bends. This design allows for the sensor device to have a probe structure wherein the surface interconnected with activity devices (i.e., an optical source and optical detector) is placed on one side. The reference channel is bent with a minimum optical loss, and the sensing channel has a bent structure, involving a C-bend waveguide with a maximum loss. The C-bend waveguide with a maximum loss is conformally aligned to have a trench structure with the same bending radius, designed to selectively expose the sidewall of the core layer. The local index contrast varies depending on the material in contact with the trench, resulting in a change in the optical output power of the waveguide. The sensitivity of the proposed sensor was 0 and 2070 µW/refractive index unit (RIU) for the reference and sensing channels, respectively, as the RI changed from 1.385 to 1.445 at a 1550 nm wavelength. These results suggest that the proposed structure enables efficient RI measurement through the use of a simple dip-type method.

Silicone-Based Adhesives with Highly Tunable Adhesion Force for Skin-Contact Applications.

A fundamental approach to fabricating silicone-based adhesives with highly tunable adhesion force for the skin-contact applications is presented. Liquid blends consisting of vinyl-multifunctional polydimethylsiloxane (V-PDMS), hydride-terminated PDMS (H-PDMS), and a tackifier composed of a silanol-terminated PDMS/MQ resin mixture and the MQ resin are used as the adhesive materials. The peel adhesion force of addition-cured adhesives on the skin is increased by increasing the H-PDMS molecular weights and the tackifier content, and decreasing the H-PDMS/V-PDMS ratio. There is an inverse relationship between the adhesion force and the Young's modulus. The low-modulus adhesives with a low H-PDMS/V-PDMS ratio exhibit enhanced adhesion properties. The low-modulus adhesives with the high MQ resin content show significantly enhanced adhesion properties. These adhesives exhibit a wide range of modulus (2-499 kPa), and their adhesion force (0.04-5.38 N) is superior to commercially available soft silicone adhesives (0.82-2.79 N). The strong adhesives (>≈2 N) provide sufficient adhesion for fixing the flexible electrocardiogram (ECG) device to the skin in most daily activity. The human ECG signals are successfully recorded in real time. These results suggest that the silicone-based adhesives should be useful as an atraumatic adhesive for the skin-contact applications.

Attogram mass sensing based on silicon microbeam resonators.

Using doubly-clamped silicon (Si) microbeam resonators, we demonstrate sub-attogram per Hertz (ag/Hz) mass sensitivity, which is extremely high sensitivity achieved by micro-scale MEMS mass sensors. We also characterize unusual buckling phenomena of the resonators. The thin-film based resonator is composed of a Si microbeam surrounded by silicon nitride (SiN) anchors, which significantly improve performance by providing fixation on the microbeam and stabilizing oscillating motion. Here, we introduce two fabrication techniques to further improve the mass sensitivity. First, we minimize surface stress by depositing a sacrificial SiN layer, which prevents damage on the Si microbeam. Second, we modify anchor structure to find optimal design that allows the microbeam to oscillate in quasi-one dimensional mode while achieving high quality factor. Mass loading is conducted by depositing Au/Ti thin films on the local area of the microbeam surface. Using sequential mass loading, we test effects of changing beam dimensions, position of mass loading, and distribution of a metal film on the mass sensitivity. In addition, we demonstrate that microbeams suffer local micro-buckling and global buckling by excessive mass loading, which are induced by two different mechanisms. We also find that the critical buckling length is increased by additional support from the anchors.

Integrated Flexible Electronic Devices Based on Passive Alignment for Physiological Measurement.

This study proposes a simple method of fabricating flexible electronic devices using a metal template for passive alignment between chip components and an interconnect layer, which enabled efficient alignment with high accuracy. An electrocardiogram (ECG) sensor was fabricated using 20 µm thick polyimide (PI) film as a flexible substrate to demonstrate the feasibility of the proposed method. The interconnect layer was fabricated by a two-step photolithography process and evaporation. After applying solder paste, the metal template was placed on top of the interconnect layer. The metal template had rectangular holes at the same position as the chip components on the interconnect layer. Rectangular hole sizes were designed to account for alignment tolerance of the chips. Passive alignment was performed by simply inserting the components in the holes of the template, which resulted in accurate alignment with positional tolerance of less than 10 µm based on the structural design, suggesting that our method can efficiently perform chip mounting with precision. Furthermore, a fabricated flexible ECG sensor was easily attachable to the curved skin surface and able to measure ECG signals from a human subject. These results suggest that the proposed method can be used to fabricate epidermal sensors, which are mounted on the skin to measure various physiological signals.

Application of thermal initiator for characteristic improvements of polymeric replica mold for UV nanoimprint lithography.

We report the improvement of the hardness and modulus properties in a silsesquioxane-based soft replica mold by adding thermal initiator, without deteriorating the UV transmittance at the wavelength of 365 nm. It is found that thermal initiator used for this work contributes to improving the hardness and modulus values up to 0.175 and 3.585 GPa, while the UV transmittance value is still above 75%. The optimized soft replica mold built on a flexible plastic substrate allows submicron-scale patterns to be transferred onto a rigid Si substrate by means of UV-NIL process. Consequently, we demonstrate that the developed soft replica mold can be a suitable replacement for typical hard molds, promising further use in mold-based nanolithography for the fabrication of high-resolution nanopatterns over large areas.

Optical interconnection for a polymeric PLC device using simple positional alignment.

This study proposes a simple cost-effective method of optical interconnection between a planar lightwave circuit (PLC) device chip and an optical fiber. It was conducted to minimize and overcome the coupling loss caused by lateral offset which is due to the process tolerance and the dimensional limitation existing between PLC device chips and fiber array blocks with groove structures. A PLC device chip and a fiber array block were simultaneously fabricated in a series of polymer replication processes using the original master. The dimensions (i.e., width and thickness) of the under-clad of the PLC device chip were identical to those of the fiber array block. The PLC device chip and optical fiber were aligned by simple positional control for the vertical direction of the PLC device chip under a particular condition. The insertion loss of the proposed 1 x 2 multimode optical splitter device interconnection was 4.0 dB at 850 nm and the coupling loss was below 0.1 dB compared with single-fiber based active alignment.

Simple fabrication of a double-layer multi-channel optical waveguide using passive alignment.

This study proposes a simple and cost-effective method of fabricating a double-layer polymeric optical waveguide, using two hot-embossing processes with a single stamp and template for passive alignment between the top and bottom layers. The two hot-embossing processes were conducted sequentially on the top layer and the bottom layer of the polymer layer. The second hot-embossing process was conducted after fabricating the buffer layer on the surface of the polymeric channel structure to control deformation and destruction of the previously fabricated polymeric channel structure. Passive alignment of the channel structure for the top layer and the bottom layer was automatically performed by simple insertion of the stamp and polymer layer using a metal template with the same dimensions (width x length) as the stamp. Regarding the polymer layer, the buffer layer on the side with the channel structure was coated, whereas the layer contacting the stamp did not have a buffer layer. For the purposes of this study, a 2 x 50 channel polymeric multimode optical waveguide was fabricated using a stamp with 50 straight ribs, without any coupling between the layers. The fabricated optical waveguide was controlled within positional tolerances of less than ± 5 µm between layers; propagation loss of below 0.2 dB/cm at 850 nm; and channel uniformity of below 0.5 dB.

Interchip link system using an optical wiring method.

A chip-scale optical link system is presented with a transmitter/receiver and optical wire link. The interchip link system consists of a metal optical bench, a printed circuit board module, a driver/receiver integrated circuit, a vertical cavity surface-emitting laser/photodiode array, and an optical wire link composed of plastic optical fibers (POFs). We have developed a downsized POF and an optical wiring method that allows on-site installation with a simple annealing as optical wiring technologies for achieving high-density optical interchip interconnection within such devices. Successful data transfer measurements are presented.