Optogenetic manipulation is widely used to selectively excite and silence neurons in laboratory experiments. Recent efforts to miniaturize the components of optogenetic systems have enabled experiments on freely moving animals, but further miniaturization is required for freely flying insects. In particular, miniaturization of high channel-count optical waveguides are needed for high-resolution interfaces. Thin flexible waveguide arrays are needed to bend light around tight turns to access small anatomical targets. We present the design of lightweight miniaturized optogentic hardware and supporting electronics for the untethered steering of dragonfly flight. The system is designed to enable autonomous flight and includes processing, guidance sensors, solar power, and light stimulators. The system will weigh less than 200mg and be worn by the dragonfly as a backpack. The flexible implant has been designed to provide stimuli around nerves through micron scale apertures of adjacent neural tissue without the use of heavy hardware. We address the challenges of lightweight optogenetics and the development of high contrast polymer waveguides for this purpose.

Wireless neural stimulators are being developed to address problems associated with traditional lead-based implants. However, designing wireless stimulators on the sub-millimeter scale (<1 mm3) is challenging. As device size shrinks, it becomes difficult to deliver sufficient wireless power to operate the device. Here, we present a sub-millimeter, inductively powered neural stimulator consisting only of a coil to receive power, a capacitor to tune the resonant frequency of the receiver, and a diode to rectify the radio-frequency signal to produce neural excitation. By replacing any complex receiver circuitry with a simple rectifier, we have reduced the required voltage levels that are needed to operate the device from 0.5 to 1 V (e.g., for CMOS) to ~0.25-0.5 V. This reduced voltage allows the use of smaller receive antennas for power, resulting in a device volume of 0.3-0.5 mm3. The device was encapsulated in epoxy, and successfully passed accelerated lifetime tests in 80°C saline for 2 weeks. We demonstrate a basic proof-of-concept using stimulation with tens of microamps of current delivered to the sciatic nerve in rat to produce a motor response.

We have fabricated polycrystalline diamond hemispheres by hot-filament CVD (HFCVD) in spherical cavities wet-etched into a high temperature glass substrate CTE matched to silicon. Hemispherical resonators 1.4 mm in diameter have a Q of up to 143 000 in the fundamental wineglass mode, for a ringdown time of 2.4 s. Without trimming, resonators have the two degenerate wineglass modes frequency matched as close as 2 Hz, or 0.013% of the resonant frequency (similar to 16 kHz). Laser trimming was used to match resonant modes on hemispheres to 0.3 Hz. Experimental and FEA energy loss studies on cantilevers and hemispheres examine various energy loss mechanisms, showing that surface related losses are dominant. Diamond cantilevers with a Q of 400 000 and a ringdown time of 15.4 s were measured, showing the potential of polycrystalline diamond films for high Q resonators. These resonators show great promise for use as hemispherical resonant gyroscopes (HRGs) on a chip.

Dynamic electrowetting on nanostructured silicon surfaces is demonstrated as an effective method for improving detection sensitivity in matrix-free laser desorption/ionization mass spectrometry. Without electrowetting, silicon surfaces comprising dense fields of oriented nanofilaments are shown to provide efficient ion generation and high spectral peak intensities for deposited peptides bound to the nanofilaments through hydrophobic interactions. By applying an electrical bias to the silicon substrate, the surface energy of the oxidized nanofilaments can be dynamically controlled by electrowetting, thereby allowing aqueous buffer to penetrate deep into the nanofilament matrix. The use of electrowetting is shown to result in enhanced interactions between deposited peptides and the nanofilament silicon surface, with improved signal-to-noise ratio for detected spectral peaks. An essential feature contributing to the observed performance enhancement is the open-cell nature of the nanofilament surfaces, which prevents air from becoming trapped within the pores and limiting solvent penetration during electrowetting. The combination of nanofilament silicon and dynamic electrowetting is shown to provide routine detection limits on the order of several attomoles for a panel of model peptides.

A new design for anisotropic piezoelectric disk resonators is demonstrated using single-crystal Al0.3Ga0.7As films. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wavelength of the desired resonance frequency. The resonators are designed with supports which emulate free-free boundary conditions. Prototype resonators are fabricated using a three-layer Al0.3Ga0.7As heterostructure containing silicon-doped electrodes and an undoped piezoelectric Al0.3Ga 0.7As layer. Quality factors as high as 11 200 are measured in air for a 23.25 MHz fundamental resonant mode, with a corresponding motional resistance of 1.67 kOmega. A finite-element model for the resonator design is also described. Simulation results agree well with both theoretical calculations and experimental data

Piezoelectric bimorph cantilever microactuators based on single-crystal Al0.3Ga0.7As are demonstrated. Fabricated devices are characterized for their quasistatic and resonant behavior when driven in both unimorph and bimorph configurations. Quasistatic actuator behavior is compared with a simple analytic model. Measured unimorph and bimorph tip deflections match well with the model, with deviations resulting from imperfections in device geometry and electrical resistivity of the electrodes. The effects of bimorph actuation on linearity and structural damping at resonance are also evaluated.

This paper reports the modeling, fabrication, and experimental characterization of piezoelectric longitudinal mode bar resonators based on thin film single crystal Al/sub 0.3/Ga/sub 0.7/ As. Fabricated resonators with lengths ranging from 1000 /spl mu/m to 100 /spl mu/m have been characterized for operation in their first five odd longitudinal modes. Resonance frequencies range from 2.5 to 75 MHz, with quality factors up to 25 390 at 21.8 MHz in vacuum. Power handling capacity as high as -2.6 dBm is demonstrated at 18.8 MHz. Motional resistance and temperature stability of the resonators are also evaluated.

A process has been developed for the fabrication of single crystal AlGaAs-based MEMS to exploit the inherent piezoelectric transduction of this material for microsensors and microactuation. The process combines molecular beam epitaxial growth of a three-layer single-crystal Al0.3Ga0.7As heterostructure on a GaAs substrate, inductively coupled plasma reactive-ion etching, and selective wet etching of GaAs to produce released Al0.3Ga0.7As beams with integrated electrodes and piezoelectric layers. The process has been validated through the fabrication of both cantilever and doubly clamped beam test structures ranging from 80 to 120μm in length, up to 15μm in width, and oriented at angles ranging from 5° to 90° relative to the (110) plane. The transverse piezoelectric coupling coefficient d31 has been measured in released devices as a function of beam orientation using both quasistatic and resonance matching methods, with good agreement to theoretical predictions.

A new process has been developed for the fabrication of AlGaAs-based MEMS which the inherent piezoelectric transduction present in this material to be used for sensing and actuation. The process combines molecular beam epitaxial growth of single-crystal Al0.3Ga0.7As multilayer, inductively coupled plasma reactive-ion etching (ICP-RIE), and highly selective wet etching of GaAs to produce released Al0.3Ga0.7As structures. The process has been validated through the fabrication of both cantilever and doubly clamped beam structures, and has wider use for applications where large electromechanical coupling strength and single-crystal heterostructure are desired.

Piezoelectric resonators based on epitaxially-grown Al0.3Ga0.7As have been developed. The resonators are fabricated using a single crystal device structure, with differential doping used to create either piezoelectric or electrode regions. Constitutive layers consist of 0.5μm Si-doped Al0.3Ga0.7As acting as the top electrode layer, 1μm undoped Al0.3Ga0.7As as the piezoelectric layer, and 2μm Si-doped Al0.3Ga0.7As as both the structural and the bottom electrode layer. Resonator fabrication employs a 4 mask process combining inductively coupled plasma reactive-ion etching (ICP RIE) and a highly selective bulk GaAs wet etching process. The frequency response of fabricated beam resonators has been measured using laser Doppler vibrometery (LDV). Both cantilever and doubly-clamped beam resonators have been demonstrated, with fabricated resonators center frequencies showing excellent agreement compared to designed values. The transverse piezoelectric coupling coefficient d31 has also been measured as a function of beam orientation.