Frank T. Hartley

Design and process considerations for a tunneling tip accelerometer

In this paper, we discuss the fabrication and initial testing of a bulk micromachined single axis accelerometer. The accelerometer is designed to have a full scale range of and a sensitivity of . Three distinctly different dice are fabricated during the process and are subsequently assembled using an alloy bonding technique. Electrical contacts are made between layers during the bonding operation. The accelerometer is controlled by electrostatic force plates above and below the proof mass. The lower electrode has a dual role. In operation, it provides a necessary control electrode. When not in operation, it is used to immobilize the proof mass.

Nanometer X-ray lithography

New developments for x-ray nanomachining include pattern transfer onto non-planar surfaces coated with electrodeposited resists using synchrotron radiation x-rays through extremely high-resolution mask made by chemically assisted focused ion beam lithography. Standard UV photolithographic processes cannot maintain sub-micron definitions over large variation in feature topography. The ability of x-ray printing to pattern thin or thick layers of photoresist with high resolution on non-planar surfaces of large and complex topographies with limited diffraction and scattering effects and no substrate reflection is known and can be exploited for patterning microsystems with non-planar 3D geometries as well as multisided and multilayered substrates. Thin conformal coatings of electro-deposited positive and negative tone photoresist have been shown to be x-ray sensitive and accommodate sub-micro pattern transfer over surface of extreme topographical variations. Chemically assisted focused ion beam selective anisotropic erosion was used to fabricate x-ray masks directly. Masks with feature sizes less than 20 nm through 7 microns of gold were made on bulk silicon substrates and x-ray mask membranes. The technique is also applicable to other high density materials. Such masks enable the primary and secondary patterning and/or 3D machining of Nano-Electro-Mechanical Systems over large depths or complex relief and the patterning of large surface areas with sub-optically dimensioned features.

Micropump technology and applications

This paper describes reversed engineered biological peristaltics through the insightful evolution of MEMS technology. While the emphasis on pump applications is in the miniaturization of spacecraft bus and payload, terrestrial applications are evident. For spacecraft propulsion, the use of the peristaltic pump as a low leakage valve, a pressure regulator and a flow meter are discussed. Spacecraft stabilization is addressed through a fluidic reaction wheel while thermal management of spacecraft, flight instruments and lander is addressed through heat pumps and Joule-Thompson compressors.

Grating fabrication through x-ray lithography

Blazed gratings have been fabricated using gray-scale X-ray lithography. The gratings have high efficiency, low parasitic light, and high groove quality. They can be generated over a considerable depth for use anywhere in the ultraviolet to middle infrared range. They can also be recorded on substrates of considerable curvature.

Focused ion beam direct micromachining of DOEs

We discuss here the capability of direct manufacture of various high- resolution diffractive optics, in particular regarding micromachining of DOEs in 3D. Preliminary demonstrations were made in 2-D using an automated FIB system operated at 30 KeV with a Gallium liquid metal ion source and equipped with a gas injection system (GIS). Gratings with a 20 nm line width and zone plates with 32 nm outer ring were milled in a reactive atmosphere (iodine) directly through 3.5 (mu) m and 800 nm of gold respectively. Plans for combining FIB and X-ray lithography to make diffractive optical elements (DOEs) for JPL are also mentioned.

A nanoscale soft-ionization membrane: A novel ionizer for ion mobility spectrometers for space applications

The Jet Propulsion Laboratory (JPL) has developed a novel nanometer-thick “Soft Ionization Membrane” (SIM) which is capable of ionizing nearly 100% of the gases that pass through it. Both sides of the membrane are coated with a metallic conducting film. A modest potential of less than 10 Volts across the membrane produces an electric field in excess of 107 V/cm over a region that is smaller than the mean free path of gas molecules which ionizes the neutral molecules that passing through. Because the region of high electric field is smaller than the mean free path of gas molecules, there are virtually no high energy collisions and the system does not suffer from the fatal problem of avalanche breakdown. The soft ionization mechanism does not fracture the medium or cause any secondary ionization. Thus, a truly new ionization technique is enabled by a simple nanoscale micromachined device. The SIM is tiny, rugged and well suited for a wide variety of applications ranging from space micropropulsion systems to miniature analytical separation devices. In this paper we focus our attention on ion mobility spectrometers (IMSs) as a potential candidate to be incorporated with SIM.

Development and terrestrial applications of a nano-g accelerometer

The ultra-sensitive accelerometer, developed for NASA to monitor the microgravity environments of Space Shuttle, free orbitors and Space Station, needed to measure accelerations up to 10 mg with an absolute accuracy of 10 nano-g for at least two orbits to resolve accelerations associated with orbital drag. Also, the accelerometers needed to have less than 10-9 F.S. off-axis sensitivity; to be thermally and magnetically inert; to be immune to quiescent shock, and to have an in-situ calibration capability. The utilization of these accelerometers in multi-axis compact seismometers designs that have twelve decades of dynamic range, density profilometers, precision gradiometers, gyros and vibration isolation designs and applications will be discussed. FInally, examples of the versatility of the proof mass suspension system will be demonstrated through the transformation of the basic accelerometer into sensitive anemometers and imaging spectrometers.

Tunneling tip protection for a bulk micromachined accelerometer

Ultrasensitive accelerometers are needed by NASA for the measurement of orbital drag. We have designed an accelerometer capable of measuring 10-8. In this paper, a method for fabricating a bulk micromachined accelerometer which incorporates a tunneling tip is presented. To meet sensitivity sepcifications, a weak spring and large mass are needed. However, these represent a delicate mechanism and a method of protection is provided by electrostatically clamping the proof mass in a fixed position. The effectiveness of the electrostatic clamp has been measured. It is found that clamping against an acceleration of 200 g is possible with voltages as low as 30 volts.

Maskless 3D micromachining with focused ion beam of high-resolution diffractive optics

We discuss here the capability and details of direct manufacture of various high-resolution diffractive optics using focused ion beam (FIB) micromachining. In preliminary demonstrations illustrating the capability of the technique, zone plates and gratings were milled in gold using a reactive atmosphere in an automated FIB system operating at 30 keV with a Gallium liquid metal ion source equipped with an iodine beam gas injection system (GIS). Gratings with 20 nm line width and zone plates with 32 nm outer ring were milled directly through 3.5 micrometer and 800 nm of gold respectively.

X-ray exposures of electrodeposited photoresist for conformal lithography on corrugated surfaces

Proximity printing using synchrotron x-ray lithography provides high resolution pattern transfer with large depth of field, low diffraction effects and no reflection form the substrate. Electro-plating of photo-resist allows deposition of thin, uniform films over geometrically complex and topographically diverse, electrically conductive surfaces. Two electro-deposited photoresists produced by Shipley, EAGLE 2100 ED negative tone and PEPR 2400 positive tone resist, have been tested with x-rays demonstrating micron pattern transfer over depths-of-field in fractions of millimeters.