Sam Y. Bae

High performance MEMS micro-gyroscope

This paper reports on JPLs on-going research into MEMS gyroscopes. [1-4] This paper will describe the gyroscopes fabrication- methods, a new 8-electrode layout developed to improve performance and performance statistics of a batch of six gyroscopes (of the 8- electrode design) recently rate tested. Previously in our group, T. Tang and R. Gutierrez presented the results of their extensive use of ethylene diamine pyrocatechol (EDP) to deep-etch the inertial- sensitive r4esonators and post-supporting structures in a 4- electrode gyroscope design. Today, JPL is utilizing an in-house STS DRIE, replacing the old wet-etching steps. This has demonstrated superior precision in machining symmetry of the resonators, thus significantly reducing native rocking mode frequency splits. A performance test of six gyros has shown an average, un-tuned, frequency split of 0.4% (11Hz split for rocking modes at 2.7KHz). The new JPL MEMS gyroscope has a unique 8-electrode layout, whose large electrodes can provide significant electrostatic softening of the resonators springs. This allows matching of the Coriolis sensitive rocking modal frequencies to be improved from the native 0.4% to an average tuned frequency split of 0.02%. In separate tests, electrostatic tuning in the 8-electrode design has demonstrated the ability to match frequency-splits to within 10mHz, thus ensuring full degeneracy in even a very high Q device. In addition, a newly selected ceramic package-substrate has improved the devices dampening loses such that a mean Q of 28,000 was achieved in the six gyroscope tested. These Qs ere measured via the ring-down time method. The improved fabrication development and other modifications described have led to the JPLs MEMS gyroscope achieving an average bias instability (Allan variance 1/f floor estimate) of 11degree/hr with best in the group being 2degree/hr. In an independent test, Honeywell Inc. reported one of our MEMS gyroscopes as achieving 1degree/hr bias instability flicker floor estimate measured at constant temperature.

3D Imaging with a Single-Aperture 3-mm Objective Lens: Concept, Fabrication and Test

There are many advantages to minimally invasive surgery (MIS). An endoscope is the optical system of choice by the surgeon for MIS. The smaller the incision or opening made to perform the surgery, the smaller the optical system needed. For minimally invasive neurological and skull base surgeries the openings are typically 10-mm in diameter (dime sized) or less. The largest outside diameter (OD) endoscope used is 4mm. A significant drawback to endoscopic MIS is that it only provides a monocular view of the surgical site thereby lacking depth information for the surgeon. A stereo view would provide the surgeon instantaneous depth information of the surroundings within the field of view, a significant advantage especially during brain surgery. Providing 3D imaging in an endoscopic objective lens system presents significant challenges because of the tight packaging constraints. This paper presents a promising new technique for endoscopic 3D imaging that uses a single lens system with complementary multi-bandpass filters (CMBFs), and describes the proof-of-concept demonstrations performed to date validating the technique. These demonstrations of the technique have utilized many commercial off-the- shelf (COTS) components including the ones used in the endoscope objective.

Silicon Nanotips Antireflection Surface for Micro Sun Sensor

We have developed a new technique to fabricate antireflection surface using silicon nano-tips for use on a micro sun sensor for Mars rovers. We have achieved randomly distributed nano-tips of radius spanning from 20 nm to 100 nm and aspect ratio of ∼200 using a two-step dry etching process. The 30° specular reflectance at the target wavelength of 1 μm is only about 0.09 %, nearly three orders of magnitude lower than that of bare silicon, and the hemispherical reflectance is ∼8%. By changing the density and aspect ratio of these nanotips, the change in reflectance is demonstrated. Using surfaces covered with these nano-tips, the critical problem of ghost images that are caused by multiple internal reflections in a micro sun sensor was solved.

Toward a 3D endoscope for minimally invasive surgery

Minimally invasive surgery (MIS) has advantages over standard surgical techniques. Because of the small opening, the recovery time is much shorter, there is less scarring, and fewer complications arise from infections. During MIS, surgeons use endoscopes to view the internal surgical site, and the smaller the endoscope, the better. For MIS neurological and skull base surgeries, for instance, the surgical opening is typically 10mm in diameter, which requires an endoscope of 4mm or less across. However, a significant drawback to endoscopic MIS, particularly during brain surgery, is that the surgeon lacks depth information that a stereo (3D) view would provide instantaneously. Human left and right eyes see the world from slightly different angles, and the disparity between them is interpreted as depth by the brain. A 3D camera mimics this by arranging two cameras. However, when the two-camera set-up is scaled down to fit a confined space smaller than a fingertip, compactness becomes an issue. Some patented solutions to this problem create a dual aperture in a single lens and alternately open the apertures to conserve space.1–6 However, until now there has been no good mechanism to alternately open the apertures in real time on this scale, which is necessary to prevent the image fields captured by both of the apertures from overlapping. This is to maximize the spatial resolution of the imaging chip: each of the dual apertures yields an image field that is as big as the imaging chip, and thus the apertures must be alternated. One approach puts shutters (mechanical and electro-optical) at the apertures. However, their mechanisms are too large to be integrated into a small lens system. Another solution consists of coupling a pair of orthogonal polarizers or a pair of complementary single bandpass filters with corresponding illuminations, which alternately open or block the apertures. Because the effective viewpoint switching occurs outside the lens, this scheme has the advantage of not increasing the lens volume. However, as the polarization Figure 1. Actual transmission plots of the complementary multiband bandpass filters. The bell curves superimposed are the multispectral light bands used in a series of illuminations.

MEMS technology at NASA's Jet Propulsion Laboratory

The MEMS Technology Group is part of the Microdevices Laboratory (MDL) at the Jet Propulsion Laboratory (JPL). The group pursues the development of a wide range of advanced MEMS technologies that are primarily applicable to NASAs robotic as well as manned exploration missions. Thus these technologies are ideally suited for the demanding requirements of space missions namely, low mass, low power consumption and high reliability, without significant loss of capability. End-to-end development of these technologies is conducted at the MDL, a 38,000 sq. ft. facility with approximately 5500 sq. ft. each of cleanroom (class 10 - 100,000) and characterization laboratory space. MDL facilities include computer design and simulation tools, optical and electron-beam lithography, thin film deposition equipment, dry and wet etching facilities including Deep Reactive Ion Etching, device assembly and testing facilities. Following the fabrication of the device prototypes, reliability testing of these devices is conducted at the state-of-the-art Failure Analysis Laboratory at JPL.

4-mm-diameter three-dimensional imaging endoscope with steerable camera for minimally invasive surgery (3-D-MARVEL).

Abstract. High-resolution three-dimensional (3-D) imaging (stereo imaging) by endoscopes in minimally invasive surgery, especially in space-constrained applications such as brain surgery, is one of the most desired capabilities. Such capability exists at larger than 4-mm overall diameters. We report the development of a stereo imaging endoscope of 4-mm maximum diameter, called Multiangle, Rear-Viewing Endoscopic Tool (MARVEL) that uses a single-lens system with complementary multibandpass filter (CMBF) technology to achieve 3-D imaging. In addition, the system is endowed with the capability to pan from side-to-side over an angle of ±25  deg, which is another unique aspect of MARVEL for such a class of endoscopes. The design and construction of a single-lens, CMBF aperture camera with integrated illumination to generate 3-D images, and the actuation mechanism built into it is summarized.