Color cathode ray tubes (CRT) have been dominating the display market for more than forty years. The unique advantages, such as high brightness, very wide viewing angle, and excellent color purity, makes all other display devices very difficult to compete with. Meanwhile, to improve the performance of CRTs and to meet the challenge of large size CRTs, modifications have been made on all components including shadow mask, bulb design, electron gun design, and yoke design. Basically, the technology improvements can be categorized into two areas: structure and ergonomics. Structurally, efforts have been concentrating towards a flatter faceplate and a finer pitch. These improvements lead to the extensive uses of low thermal expansion shadow mask and higher resolution gun design. An alternative improvement is the introduction of tensioned mask CRTs. In the area of ergonomics, efforts are focusing on the improvements of contrast and resolutions such as the introduction of antireflective and antistatic function on the faceplate. Details will be presented in this ppaer.
We report on novel 3D tunable Fabry-Perot etalons fabricated by surface micromachining technique. The Fabry-Perot etalons are tuned by rotation or translation movements. For the Fabry-Perot etalon tuned by rotational movement, the Fabry-Perot etalon is integrated with a rotational stage and the effective light path distance is adjusted by rotating the stage. The transmission peak wavelength shift (Delta) (lambda) p of 32 nm has been observed for tuning angle (Delta) (Theta) equal to 70 degrees. For the Fabry-Perot etalon tuned by linear translation, two mirrors consitituting the etalon are integrated with translational stages. The stage consists of a slider constrained by flanges along the two edges so that only translational movement along the optical axis is allowed. By changing the distance between two mirrors for 2.25 micrometers , a transmission peak wavelength shift (Delta) (lambda) p of 103 nm has been achieved. The 3D Fabry-Perot etalons can be easily extended to integrate with other micro- optical elements fabricated in a similar way. Furthermore, fiber-to-fiber coupling will be easy with this 3D approach. The 3D tunable Fabry-Perot etalon is another successful demonstration of the free-space micro-optical bench (FS-MOB) technology we have proposed previously.
A thermo-optic modulator/switch has been fabricated using the antiresonant reflecting optical waveguide. The device is based on a Mach-Zehnder interferometer with a thin film metal heater placed in the vicinity of one of its arms. Preliminary tests reveal that the device has a good on-off ratio with a switching response time of 1 ms.
The basic aim of this work is to obtain optical detectors with a spectral response programmable by design using the combined response of polysilicon and monocrystalline silicon photodiodes. Such an approach is needed in order to obtain a color sensor with improved flexibility and control of its characteristic parameters. In order to achieve this aim, the potential of different multilayer thin film light detectors has been evaluated. The results show that polysilicon diodes can be realized and used as light detectors and a simple test structure has been fabricated in order to demonstrate the possiblity of implementing thin film color detecting structures.
We report a novel fiber data distribution interface (FDDI) optical bypass switch using the surface-micromachining technology. In this design, all of the switches' components are made of polysilicon films and are monolithically patterned. The switch consists of four multimode optical fibers and a two-sided mirror sitting vertically on the top of a sliding plate which can be driven by an integrated micro-actuator. The gap between two in-line fibers are minimized to reduce insertion loss without using any lense. The total insertion loss of the switch has been measured to be 2.8 dB for the CROSS state and 3.1 dB for the BAR state with a LED source operates at 1.3 micrometers wavelegnth. The cross-talk between two states is measured to be 26.1 dB. The insertion loss and cross-talk can be improved further using different designs. Using this approach, the size, weight, and cost of current FDDI bypass switches can be dramatically reduced. Furthermore, the micromachined FDDI bypass switches are potentially integrable with the optical sources/detectors and controlling electronics.
Directional couplers based on antiresonant reflecting optical waveguides (ARROW) have been fabricated and tested. The exchange of power from one waveguide to the other could be well controlled by adjustment of geometrical parameters such as the coupling length and/or the etch depth of the rib ARROW waveguide. Simulations based on the beam propagation method yield good agreement with measurement data and has been found to be indispensable for accurate design and analysis of ARROW directional couplers. Owing to the ARROW structure, the directional couplers presented have the feature that they also perform the polarizing function.
Miniature all-fiber phase modulators have been fabricated by integrating piezoelectric actuator coatings with telecommunication optical fibers. Evaporation and sputter deposition processes were used to grow thin film PbZrxTi1 - xO3 (PZT) and ZnO actuator structures directly on the surface of optical fibers. When an electric field is applied to the piezoelectric coating, a strain is produced in both the coating and the optical fiber. The strain induced in the optical fiber causes a change in the refractive index through the photoelastic effect. Electric field tuneable optical phase modulation was achieved by utilizing the optical path length changes in the optical fiber that are induced by the integrated actuator structure. Processes similar to those used for coating optical fibers were also used make micro-tubes of PZT and ZnO between 20 and 30 micrometers in diameter. The piezoelectric layers were deposited onto polyester fibers, which were subsequently burned away to leave behind a micro-tube. Actuator structures have been produced and show promise for micro-electro- mechanical applications.
The DMD is a semiconductor light switch which is making an impact in digital light processingTM (DLP) applications. It is the world's largest micro-electro-mechanical structures (MEMS) device with chips ranging from 442-thousand to 2.3 million moving mirrors. The DMD operates in a bistable (binary) mode and fully supports the movement to all-digital display systems. Currently, DMD devices are being used to develop a family of projection display products. An overview of digital light processing systems will be given with emphasis on the performance of the first prototypes using this technology, including their value propositions. Finally, the general markets served by this technology, along with the advantages DMD technology offers, will be discussed.
Hexagonal micromirror arrays and associated test structures have been fabricated using a commercial surface-micromachining process. The hexagonal micromirrors are 50 micrometers across and are arranged in a hexagonal array of 127 mirrors with 75 micrometers center-to-center spacing between nearest micromirrors. Each micromirror is supported by three flexure hinges, each of which surrounds one third of the micromirror perimeter. Each micromirror in the array can be displaced independently through a vertical distance of over 1 micrometers by a voltage applied to an underlying address electrode. The flexures and other highly diffracting or poorly reflecting areas can be covered by a statinary reflecting plate with holes that expose the moving micromirrors. These micromirror arrays function as efficient phase-mostly spatial light modulators. Applications for these micro-opto-electro-mechanical systems include optical processing, coherent beam shaping, and adaptive optics. This design has several important advantages. First, the hexagonal micromirror and array geometries maximize the active surface area of the array. Second, the use of three flexures instead of four, as is typical for square phase-mostly micromirrors, lowers the required drive voltage. Third, the reflecting cover plate ensures that light efficiency is maximized and that a substantial stationary coherent reference plane is provided. Design considerations for fabricating the arrays in commercial surface mciromachining processes are discussed. The deflection versus voltage behavior of the hexagonal micromirror is determined analytically and experimentally. Test results are used to design the next generation array.
A 100 X 100 micrometers 2 aluminum micromirror is designed and fabricated using a thick photoresist as a sacrificial layer and as a mold for nickel electroplating. The micromirror is composed of aluminum mirror plate, two nickel support posts, two aluminum hinges, and two address electrodes. The aluminum mirror plate, which is suppoorted by two nickel support posts, is overhung about 10 micrometers from the silicon substrate. We use thick photoresist to obtain 10 micrometers thick sacrificial layer and electroplate nickel to obtian 10 micrometers height support post. The aluminum mirror plate is actuated like a seesaw by electrostatic force generated by electrostatic potential difference applied between the mirror plate and the address electrode. We use reactive ion etching to release the micromirror plate from the silicon substrate. The edge of the mirror plate landed on the substrate (maximum deflection) when the potential difference between the mirror plate and the address electrode was 35 volts, and the mirror was released from the substrate when the potential difference reduced to 22 volts.
A new class of silicon-based deformable mirror for use in optical applications such as adaptive optical systems and optical correlators is being built. The mirror will be a massively parallel system of electrostatically controlled, interconnected microactuators that can be coordinated to achieve precise actuation and control at a macroscopic level. The deformable mirror system described here will be made up of a planar array of 400 electrostatically actuated actuators, which actuate a laterally continuous mirror at discrete points, resulting in surface-normal deflection of up to 4 micrometers . Several generations of single actuators as well as arrays of actuators with a mirror sheet over them have been designed, fabricated, and tested. Deflection characteristics and pull-in behavior of the actuators have been closely studied. Tests for yield, reliability, resolution, and frequency response have given optimistic results. Numerical models of the system have been developed and results from the numerical simulations agree well with experimental results.
We describe a new technology which is appropriate for the production of lightweight, highly compact displays. It is based upon a thin layer of ferroelectric liquid crystal (FLC) on top of, and directly driven by, an active matrix backplane fabricated on single crystal silicon. While devices can be produced using fairly standard techniques, we have developed custon fabrication and packaging techniques, required for optimization of optical quality and performance. We have successfully developed the technology for spatial light modulators for use in applications such as optical correlators and programmable holograms. The FLC is configured in the binary surface stabilized configuration: the CMOS circuits are digital in nature. The device operates in reflection with each pixel having an aluminium pad which acts as a mirror to reflect light and as an electorde to control the state of the overlying FLC. The technology also shows promise as a display technology so we have demonstrated the devices as displays capable of displaying both grey scale and color. We have built FLC devices upon commercially fabricated wafers but have found it advantageous to carry out custom post processing order to improve performance. The main thrust to date has been the use of ECR oxide deposition followed by chemical mechanical polishing to provide an optically flat substrate for mirror deposition. This allows the deposition of flat mirrors which fill almost all of the pixel area; it also allows optimization of the mirror deposition for high optical quality and good FLC alignment. Work is also well advanced on a technique to fill the vias connecting to the mirror layer and on packaging devices to reduce bowing of the silicon and increase the thickness uniformity of the FLC layer. Recent results are demonstrated on LCDs fabricated above two silicon backplanes containing 176 X 176 pixels and 256 X 256 pixels respectively, the former having dynamic signal storage at each pixel, the latter static storage.
Xenon difluoride is a gas phase, room temperature, isotropic silicon etchant with extremely high selectivity to many materials commonly used in microelectromechancial systems, including photoresists, aluminum, and silicon dioxide. Using a simple vacuum system, the effects of etch aperture and loading were explored for etches between 10 and 200 micrometers . Etch rates as high as 40 micrometers /minute were observed. Initial characteriation of wafer surface temperature during the etch indicates tens of degrees of self-heating, which is known to cause substantial decrease in etch rate.
Proc. SPIE 2641, Post-processing using microfabrication techniques to improve the optical performance of liquid crystal over silicon backplane spatial light modulators, 0000 (13 September 1995); doi: 10.1117/12.220934
Liquid crystal (LC) over silicon backplane spatial light modulators (SLMs) have applications in optical processing and as miniature displays. With these devices a LC layer is sandwiched between the silicon backplane and a front cover glass coated with a transparent ITO electrode. The voltage between electrodes on the controlling circuitry and the ITO electrode determines the state of the LC which in turn is used to modulate incident light onto the device. The silicon backplane consists of an array of pixels similar to DRAM or SRAM devices but where each pixel controls the voltage on an electrode. These electrodes must also act as mirrors reflecting the incident light. The silicon backplanes supplied by commercial foundries which work well electrically suffer from having poor optical quality pixel mirrors. These mirrors have inferior surface quality with low flat fill factor resulting in low optical efficiency. Hillocks are also present which cause problems with LC cell construction. We have developed a post-processing procedure based on silicon microfabrication techniques to add another level of metal to commercially fabricated wafers which addresses these problems. To ensure that his new metal layer is deposited onto a very flat substrate the interlevel dielectric is planarized using chemical mechanical polishing. We have developed this technique to produce an optical quality surface with local surface variations of less than 100 angstrom consistently achieved. The deposited aluminium top layer is optimized for best optical performance within the constraints of the electrical characteristics. Pixel mirrors with flat fill factors up to 84% were realized which improved the optical efficiency of the SLM. No hillocks were present on the metal surface presenting the opportunity to fabricate 1 micrometers thick LC cells to fully utilize the potential of ferroelectric LC. We will also report on a n expansion of the post-processing procedure to protect devices based on DRAM memory layout from photo induced charge leakage. The use of microfabrication techniques to construct the LC spacer layer will also be discussed.
High aspect-ratio single-crystal microtips have been fabricated using the semi-anisotropic dry etching technique. After the further oxidation sharpening process, arrays of 50 X 50 uniform sharp emitter tips has been achieved. The 200 angstrom-thick Cr metal was also coated on the surface of Si microtips to improve the performance. Furthermore, a modified self-aligned process of the gated field emitter arrays has been successfully developed to reduce the fabrication complexity. Employing this method, the tip radius of Si microemitter is about 200 angstrom, and the gate aperture can be easily reduced to about 0.3 micrometers . It will largely decrease the turn-on voltage of the field emission devices.
The structure of Pd-silicided field emitters based on the silicon micromachining technology has been demonstrated. The uniform and extremely sharp silicided emitters are formed using wet chemical etching, low-temperature oxidation sharpening, coating metal and furnace annealing in N2 ambient. The sheet resistance and Auger electron spectroscope results depict the transformation of silicidation. Transmission electron microscope of bright-field, dark-field, and diffraction pattern show the formation of silicided emitters. These emitters have potential applications in vacuum microelectronics to obtain superior lifetime, relaibility, and stability.
Projection displays and microelectromechanical systems (MEMS) have evolved independently, occasionally crossing paths as early as the 1950s. But the commercially viable use of MEMS for projection displays has been illusive until the recent invention of Texas Instruments Digital Light Processing TM (DLP) technology. DLP technology is based on the Digital Micromirror DeviceTM (DMD) microchip, a MEMS technology that is a semiconductor digital light switch that precisely controls a light source for projection display and hardcopy applications. DLP technology provides a unique business opportunity because of the timely convergence of market needs and technology advances. The world is rapidly moving to an all- digital communications and entertainment infrastructure. In the near future, most of the technologies necessary for this infrastrucutre will be available at the right performance and price levels. This will make commercially viable an all-digital chain (capture, compression, transmission, reception decompression, hearing, and viewing). Unfortunately, the digital images received today must be translated into analog signals for viewing on today's televisions. Digital video is the final link in the all-digital infrastructure and DLP technoogy provides that link. DLP technology is an enabler for digital, high-resolution, color projection displays that have high contrast, are bright, seamless, and have the accuracy of color and grayscale that can be achieved only by digital control. This paper contains an introduction to DMD and DLP technology, including the historical context from which to view their developemnt. The architecture, projection operation, and fabrication are presented. Finally, the paper includes an update about current DMD business opportunities in projection displays and hardcopy.
The rapid expansion in number and scope of research projects in the general area of micromachining technology makes the field especially interesting. Advances, particularly from universities and research institutes, suggest that increased commercial development is likely in a number of new fields. The nature of the fabrication technologies used to make these prototype parts, however, lead to difficulties in quickly reaping commercial benefits from these technolgoical advancements. This is in contrast to the nature of commercial development in the integrated circuit industry, where standardized processes result in rapid development of systems and products which use new designs.