The design, performance, and potential applications are described for capacitive transducers with curved electrodes. A curved electrode governs the deflection of a compliant electrode under applied stress. A dielectric film on one electrode provides a variable region of fixed electrode spacing. The sensitivity and linear dynamic range of the transducers are higher and wider than devices with parallel electrodes. An electrical advantage is obtained from the permittivity of the dielectric film and a mechanical advantage from its thinness. Transducers have been constructed with silicon diaphragms that bend and polymer membranes that stretch in response to uniform pressure. The silicon sensors measured dynamic pressure changes over a linear range of 125 dB. An 885% change in capacitance was obtained for a sensor with a thin silicon diaphragm. Sensors with polycarbonate membranes demonstrated the ability of a low-cost transducer to measure pressure, fluid flow, displacement, and tilt. An active capacitive bridge circuit was developed to linearly measure capacitance changes up to 1000% and to control electrostatic actuators by force-balanced feedback. Methods and materials to construct microscale transducers are discussed along with the performance limitations of electrostatic actuation.Index Terms-Capacitive transducer, curved electrode, electret transducer, electrostatic actuator, force-balanced feedback, nullbalanced bridge (NBB), ultrasound transducer.

Irising time of microchannel plaie intensifiers with quartz cathode windows has been reduced to less than 100 ps. This is achieved by application of a metal underlay to reduce cathode substrata resistance. The first approach uses a 50%-transmissive Uniform nickel heavy underlay, while the second approach uses a 96%-transmissive nickel mesh.For the heavy underlay, approximately 5 nm of nickel is evaporated over the cathode side of the quartz window. For the mesh underlay, approximately 750 nm of nickel is sputtered onto the window and coated with photoresist, which is exposed through a mask of 100-micron-square spaces defined by 3.5-micron-wide lines. The photoresist is developed and washed off, exposing the nickel covering the square areas. At this point, photoresist still covers the nickel over the 3.5-micron-wide wires, protecting them when the exposed nickel covering the squares is etched away. Removal of the remaining photoresist leaves only the nickel wires, which have been reduced to 2 microns in width due to sideways etching during removal of the squares.As a prototype effort, Lawrence Livermore National Laboratory (LLNL) purchased two 1 8-mm heavy underlay tubes from Hamamatsu Photonics and formed a mesh underlay on faceplates which Hamamatsu used for construction of two additional tubes. Measurements of irising time were made on these four tubes. Irising is characterized by a bright ring, seen first at the edge as it propagates toward the center. The time lag is caused by the distributed time constant of the substrata resistance and the cathode-to-MCP capacitance. Since the capacitance is fixed by restraints of tube geometry, our goal was to reduce the distributed resistance sufficiently to achieve sub-nanosecond irising times. Testing showed no irising on one tube of each type of underlay. With these encouraging results, LLNL and Nanostructures refined the mesh application technology, and LLNL procured eight mesh tubes from ITT using meshes formed by Nanostructures. An additional 8 tubes with a 50% transmissive heavy underlay were procured from Hamamatsu. Testing of these tubes also showed no detectable irising, which leads us to conclude that tubes can be made with irising clearly faster than the time resolution of our measurement system, which we estimate to be less than 50 Ps.

A detailed study of the resolution performance of an advanced research type ‘‘Alpha Ion Projector’’ with 5× ion-optical reduction has been performed. One part of the study was done with a nickel open stencil test mask with an active field of 40 mm×40 mm with smallest line pattern openings of ≊0.7 μm width (2.0 μm periodicity). The other part was done with a silicon stencil test mask (120 mm diam, 2.5 μm thickness, 60 mm×60 mm design field) with smallest line patterns of ≊0.4 μm width (1.0 μm periodicity). The Alpha Ion Projector exposures were performed in positive (PMMA: OEBR-1000) and negative (SNR-M4, RAY-PN) resist materials with subsequent wet chemical development. The 0.15-μm resolution was obtained in the case of wafer exposures with the nickel stencil mask within the 8 mm×8 mm exposure field whereas in the case of wafer exposures with the silicon stencil mask sub-0.1-μm resolution could be achieved near the center of the exposure field at 5.2× ion-optical reduction.

This paper describes recent developments in three areas ofmasked ion beam lithography (MIBL). These are 1) fabrication oflarge area, low distortion, silicon stencilmasks for demagnifying ion projection lithography, 2) fabrication ofstencil masks with nanometer scale resolution for 1:1 proximity printing, and 3) development of a direct method of alignment using the ion beam induced fluorescence of Si02. These topics are discussed below.Demagnifying ion projection masks: We describe the fabrication of stencil masks in large area, low stress (10 MPa), n-type silicon membranes. The projection masks have a silicon foil area 95 mm in diameter, thicknesses between 1.5-5 and resolution of0.6um. Measured distortion (3a) in the IPL masks ranges between 0.23gm and 0.65,um, with an experimental error of 0.20 1um.Proximity printing masks: A process is described for fabricating stencil masks with 50 nm resolution in low stress, n-type silicon membranes. Membranes less than 0.5 ,ttm thick are shown to be free of the sidewall taper that limits resolution in thicker masks. These thin membranes show a slightly flared profile due to the imperfectly collimated etching ions.Alignment: A direct method of alignment is being developed which uses the ion beam induced fluorescence of Si02 marks. Fluorescence yield is characterized as a function of ion energy and resist coating thickness. The yield for Si02 is in the range between 0.1-1.0 photons/proton, while the yields for Si, Al, and photoresist are negligibly small. Thus, a simple alignment technique can be implemented where registration of a grating in the mask with a corresponding oxide pattern is detected as a fluorescence maximum. A simple model predicts that 50 nm alignment can be accomplished, following a 1 im prealignment, in 2 seconds.