Chip-scale atomic devices

Chip-scale atomic clocks and sensors combine elements of precision atomic spectroscopy, silicon micromachining and photonics technology to achieve good performance with small size and low power consumption. Recent advances will be discussed including compact optical clocks, micromachined atomic beam clocks. Full-text article not available; see video presentation

The use of integrated circuit technology to build mechanical structures by the use of silicon micromachining has gained wide acceptance for some sensor types over the past 10 years. The principal application for silicon micromachining has been for pressure transducers used in the automotive and medical markets. The use of silicon micromachining technology in acoustical sensors has been somewhat limited, although some microphones and accelerometers have been built using this technology. This paper will review the micromachining technologies with specific application to the acoustics and acceleration sensors. Examples will be given for microphones, accelerometers, and pressure transducers with the material process technology used for their manufacture. Projections are made of future trends in silicon micromachining technology for acoustic transducers. The electronic interface to these acoustic and acceleration transducers are explored.

Solid-state microsensors and microactuators have recently become attractive for a number of instrumentation and control systems. This paper reviews some of the major and widely used silicon micromachining and microfabrication technologies, including bulk micromachining, surface micromachining, and electroplating techniques along with their applications. >

A W-band decoupling structure sandwiched between a pair of high-gain step-profiled horn array antennas using the silicon micromachining technology is proposed. To suppress the surface wave, 18 choke slots with a depth of one quarter wavelength at 94 GHz are arranged in a triangular-grid array and the isolation can be averagely improved by about 7 dB with a range of 2-20 dB. This decoupling structure and two W-band coplanar array antennas are fashioned and fully integrated together by the silicon micromachining technique. Five 400 μm thick and one 650 μm thick silicon wafers are utilized and the total thickness of the antennas is 2.65 mm. Thanks to this technology, light weight, compact size, and high integration of the decoupling structure and array antennas can also be achieved. Additionally, the two array antennas share a common ground plane within a small edge-to-edge spacing of 6.05 mm where TM surface waves exist. Experimental studies validate the performance of the proposed triangular-grid choke slot array.

We present a method of optical magnetometry with parts-per-billion resolution that is able to detect biomagnetic signals generated from the human brain and heart in Earth's ambient environment. Our magnetically silent sensors measure the total magnetic field by detecting the free-precession frequency in a highly spin-polarized alkali-metal vapor. A first-order gradiometer is formed from two magnetometers that are separated by a 3-cm baseline. Our gradiometer operates from a laptop consuming 5 W over a USB port, enabled by state-of-the-art microfabricated alkali-vapor cells, advanced thermal insulation, custom electronics, and compact lasers within the sensor head. The gradiometer has a sensitivity of 16 fT/cm/Hz1/2 outdoors, which we use to detect neuronal electrical currents and magnetic cardiography signals. Recording of neuronal magnetic fields is one of a few available methods for noninvasive functional brain imaging that usually requires extensive magnetic shielding and other infrastructure. This work demonstrates the possibility of a dense array of portable biomagnetic sensors that are deployable in a variety of natural environments.

Silicon micromachining technology will play an important role in the fabrication of high-bandwidth servo controlled microelectromechanical (mechatronic) components for super-compact disk drives. At the University of California, Los Angeles, and the California Institute of Technology, for the last three years, we have initiated a number of industry-supported joint research projects to develop the necessary technology building blocks for an integrated drive design of the future. These efforts include a silicon read/write head microgimbal with integrated electrical and mechanical interconnects, which targets the next-generation 30% form factor pico-sliders, and an electromagnetic piggyback microactuator in super-high-track-density applications, both of which utilize state-of-the-art silicon micromachining fabrication techniques.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This article presents the latest developments of our work related to a micro-lens antenna integrated in a heterodyne receiver using silicon micromachining technology at Terahertz frequencies. The antenna is composed of a waveguide feed which uses a leaky wave cavity to enhance the directivity and illuminate a shallow lens efficiently. The receiver is a dual-polarized balanced heterodyne detector using hot-electron bolometers (HEB) as mixers. The front-end receiver, including the antenna, can be fabricated using silicon micromachining processes and has seamless integration, which reduces the overall size and losses.

This paper describes a polysilicon pressure sensor fabricated by silicon micromachining technology. The starting materials of the sensor are (100) orientated monocrystal silicon wafers with double side polishing. The semiconductor integrated circuit process is also used in the testing. The polysilicon piezoresistors are deposited by LPCVD on the thermallygrown oxide film of the silicon wafer. In order to increase sensitivity, a so-called "twin isles" structure has been used. This type of structure consists of a square silicon diaphragm with twin square isles, which are formed by anisotropic etching into the back side of the monocrystal silicon substrate wafer. A main problem in preparation is the convex corner undercutting effect in the etching process. The relationships between the corner undercutting rate and the etching depth in TMAH solution have been obtained experimentally. Two masks of the special pattern are designed to compensate for corner undercutting. 1). A compensating angle bounded by &lt;210&lt; orientation is added to convex corner of twin square isles. The width of the compensation angles depends on the etching depth. 2). A narrow stripe is added to each convex corner along &lt;110&lt; orientation. The length of the narrow stripe depends on the etching depth. The optimized structures of the square diaphragm with twin square isles have been fabricated using the above two methods, respectively. Each method has its own advantages. The fabricated polysilicon pressure sensors have high sensitivity at elevated operation temperature and good accuracy. key words: silicon micromachining, comer undercutting, polysilicon pressure sensor, compensating method.

Most of the MOEMS including optical switches and micro optical benches are developed on silicon. As for the MEMS, the main reason is that silicon has consistently been the material of choice for the microelectronics industry, due to a mature processing technology which offers the possibility to integrate MEMS devices with Integrated Circuits in a low cost batch fabrication process. However, since the beginning of Optoelectronic, silicon has been suffering from its poor efficiency to emit light because of its indirect band gap. Optical active devices can be integrated on silicon by combining specific active materials in order to keep the main advantage of silicon micromachining for MOEMS applications. This paper illustrates this purpose through one project developed in the frame of the LIMMS, joint laboratory between France and Japan. This project deals with optical active devices for which silicon micromachining technology has been employed to fabricate an organic semiconductors based light emitted diode on silicon substrate.

Silicon micromachining and thin-film technology have been employed to fabricate iridium stimulating arrays which can be used to excite discrete volumes of the central nervous system. Silicon multichannel probes with thicknesses ranging from 1 to 40 microns and arbitrary two-dimensional shapes can be fabricated using a high-yield, circuit-compatible process. Iridium stimulating sites are shown to have similar characteristics to iridium wire electrodes. Accelerated pulse testing with over 8 million 100 microA biphasic current pulses on 8000 microns 2 sites has demonstrated the long-term stability of iridium and activated iridium sites. In vivo tests have been performed in the central auditory pathways to demonstrate neural activation using the devices. These tests show a selective activation both as a function of site separation and site size.

Microfabricated liquid handling elements can be regarded as key devices in very different application areas. They will play a major role in the development of innovative systems for chemical process control like µTAS, but also in medical drug delivery systems, environmental control, consumer goods or industrial equipment. Micropumps and active microvalves as the main parts of these systems are connected by closed channels together with other “plumbing” elements, like check valves, branchings, mixers or reservoirs. The progress in silicon micromachining and related micro structuring technologies like LIGA has lead to the development and successful demonstration of a multitude of devices. The current effort is to combine the appropriate liquid handling elements with chemical and biochemical transducers for the development of µTAS. This will be a hybrid system to allow the integration of components from different sources and fabricated with different technologies. Only this will lead to efficient production processes and the necessary economy of scale for successful commercial exploitation.

We present the fabrication process and the characteristics of a flexible tactile sensor by silicon micromachining, polymer processing and packaging technologies. The fabrication process for the tactile sensor was composed of in the fabrication of sensor chips and their packaging on the flexible printed circuit board (FPCB). The variation rate of resistance was about 4.6%/N when normal force was applied. This sensor can be used to sense touch, pressure, and slip because the signals are is are determined by the variations of resistance of the metal strain gauge for normal and shear force in tactile sensor.

This paper presents a broadband fully micromachined transition from rectangular waveguide to cavity-backed CPW line for submillimeter-wave (sub-MMW) and terahertz applications. A cavity-backed CPW line (CBCBW) is a planar transmission line that is designed and optimized for minimum loss while providing 50- Ω characteristic impedance. This line is shown to provide less than 0.12 dB/mm loss over the entire J-band (220-325 GHz). The transition from CBCPW to waveguide is realized in three steps to achieve a broadband response with a topology amenable to silicon micromachining. The first step is a tapered transition from the CBCPW line to a 50- Ω reduced-height waveguide. The next two steps utilize a novel in-plane impedance tapering technique to transition from the reduced-height waveguide to the on-wafer regular height waveguide. The full transition has less than 0.9 dB of insertion loss and more than 13 dB of return loss over the entire J-band (39% bandwidth). Silicon micromachining technology is used to fabricate prototypes of back-to-back CBCPW line-to-waveguide transitions. A novel waveguide-probe measurement setup is introduced and utilized to evaluate the performance of the transitions and the CBCPW lines.

This paper reports fabrication results of silicon retinal tacks and preliminary test results of silicon-micromachined retinal tacks. It is mainly intended to fix a stimulating microelectrode array, which is a part of the implantable artificial retina system. Although conventional retinal tacks made of titanium are widely used, they are expensive, invasive and restricted in shape. Also, glues could cause degeneration of inner retina and fibrin formation. Silicon micromachining technology, based on semiconductor manufacturing, can produce retinal tacks in a mass. Furthermore, the tack is easily shaped and the shapes are highly reproducible. Various types of retina tacks are proposed and fabricated. Ex vivo experiment was done in enucleated porcine eyes and in vivo experiment was done in rabbit eyes. There were some points to be improved, but we found that the silicon tack was useful and could be a good candidate as the substitute for the conventional titanium tack.

A novel integrated silicon micromachined diplexer-antenna module for compact terahertz (THz) heterodyne receiver is proposed. The module is composed of a radio frequency (RF) antenna, a local oscillator (LO) antenna, and a waveguide diplexer which are realized by using the silicon micromachining technology and stacking nine equal-thickness layers. The corrugated conical horn antenna and quasi-diagonal horn antenna are applied as the RF- and LO-antenna, respectively. The diplexer is composed of two third-order waveguide bandpass filters and an H-plane T-junction, providing the isolated RF and LO channels. An experimental study is carried out in the 340 GHz band, demonstrating its application potential in THz heterodyne receiver element and array.