Diffractive spatial optical modulators (SOM) employing a fine-pitch pixel array were introduced. The micromechanical designs of the lead zirconate titanate (PZT) actuator and mirror ribbon structure were optimized for a small volume while maintaining the same level of performance. The same design rule and fabrication equipment were used for a new 10-µm-pitch and conventional 16-µm-pitch SOM. The optical efficiency of the new SOM was 78% (zeroth-order diffraction), which is an improvement over that of the 16-µm-pitch SOM (73%). The full on/off contrast ratio showed no differences, and a high displacement of 500 nm was achieved. The stress of the Pt/PZT/Pt actuating layer was the main parameter affecting the initial gap height and displacement of the ribbon. The required ribbon flatness could be achieved by applying a stress gradient on the SiN layer. The temperature-sensitive characteristics, which degrade image quality, could be minimized by a mechanical compensation method that takes advantage of the thermal expansion effect of Si substrates. The estimated lifetime of the device is >4000 h. The developed fine-pitch SOM device has sufficient response time and ribbon displacement to be suitable for high-quality embedded laser-projection displays. The VGA optical module was successfully demonstrated in a mobile laser projection display.
Diffractive spatial optical modulators (SOM) with fine pitch pixel array were introduced for the mobile applications of
laser projection display which requires the small volume, low power consumption and high optical efficiency.
Micromechanical designs of piezoelectric (PZT) actuator and mirror ribbon structure were optimized for small volume,
but keeping the same level of the other performance. Even though the same design rule and fabrication equipment were
used for 10 um pitch SOM and 16 um pitch SOM, the optical efficiency of the fine pitch SOM was 78 % for the 0th order
diffraction and is better than that of 16 um pitch SOM (73%). The full on/off contrast ratio has no difference between 10
um pitch and 16 um pitch SOM. All the optical characteristics coincide well with the theoretical estimations. High
displacement of 500nm, which is enough to modulate the three Red, Green and Blue colors were achieved by the control
of the thicknesses and stresses of constituent structural layers. It was found that the stress of Pt/PZT/Pt actuating layer
was the main parameter affecting the initial gap height of the ribbon and also its displacement. For improving the optical
properties of the SOM devices, the required ribbon-flatness could be achieved by applying a stress gradient on the SiN
layer to compensate for the stress unbalance between Al mirror and SiN supprting layer. The temperature sensitive
characteristics of the SOM device, which degrades the image quality, could be minimized by a mechanical compensation
method using a thermal expansion effect of Si substrates. This concept could be applied in most of the bridge type
MEMS structure. The most critical parameter which limit the SOM device lifetime was found to be the ribbon
displacement degradation. By using a temperature accelerating lifetime measurement method based on the displacement
degradation the estimated lifetime was more than 4,000 hrs and is of acceptable level in the mobile application. In short,
the developed fine pitch SOM device, for making small volume of optical module, has sufficient response time and
ribbon displacement for modulating the red, blue and green colors with one SOM chip and is suitable for high quality
embedded laser projection displays. Optical module with VGA is successfully demonstrated for its potential applications
in mobile laser projection display such as a embed projection cellular phone.
A diffractive optical modulator has been fabricated based on a micromachining process. Novel
properties of its fast response time and dynamics were fully understood and demonstrated for the
strong potentials in embedded mobile laser display. Bridged thin film piezo-actuators with so called
open mirror diffraction structure has been designed. Optical level package also was achieved to
successfully prove its display application qualities. Display circuits and driving logic were developed
to finally confirm the single-panel laser display at a 240Hz VGA (640×480). With its efficiency of
more than 75% and 13cc volume optical engine with the MEMS-based VGA resolution SOM
showed 7 lm brightness at a 1.5W electrical power consumption. Detailed design principle,
fabrication, packaging and performances of the invented SOM are described.
A new type of diffractive spatial optical modulators, named SOM, has been developed by Samsung Electro-Mechanics
for laser projection display. It exhibit inherent advantages of fast response time and high-performance light modulation,
suitable for high quality embedded laser projection displays. The calculated efficiency and contrast ratio are 75 % and
800:1 respectively in case of 0th order, 67 % and 1000:1 respectively in case of ±1st order. The response time is as fast as
0.7 &mgr;s. Also we get the displacement of 400 nm enough to display full color with single panel in VGA format, as being
10 V driven. Optical module with VGA was successfully demonstrated for its potential applications in mobile laser
projection display such as cellular phone, digital still camera and note PC product. Electrical power consumption is less
than 2 W, volume is less than 13 cc. Brightness is enough to watch TV and movie in the open air, being variable up to 6
lm. Even if it's optimal diagonal image size is 10 inch, image quality does not deteriorate in the range of 5 to 50 inch
because of the merit of focus-free. Due to 100 % fill factor, the image is seamless so as to be unpleasant to see the every
pixel's partition. High speed of response time can make full color display with 24-bit gray scale and cause no scan line
artifact, better than any other devices.
In this work, the flip-chip method was used for packaging of the RF-MEMS switch on the quartz substrate with low losses. The 4-inch Pyrex glass was used as a package substrate and it was punched with airblast with 250 micrometers diameter holes. The Cr/Au seed layer was deposited on it and the vias were filled with plating gold. After forming the molds on the holes with thick photoresist, the bumps were plated on holes. The package substrate was bonded with the quartz substrate with the B-stage epoxy. The loss of the overall package structure was tested with a network analyzer and was within -0.05 dB. This structure can be used for wafer level packaging of not only the RF-MEMS devices but also the MEMS devices.
This work reports the tunneling effects of the lateral field emitters. Tunneling effect is applicable to the VMFS(vacuum magnetic field sensors). VMFS uses the fact that the trajectory of the emitted electrons are curved by the magnetic field due to Lorentz force. Poly-silicon cantilevers were used as field emitters and anode materials. Thickness of the emitter and the anode were 2μm, respectively. PSG(phospho-silicate-glass) was used as a sacrificial layer and it was etched by HF. Cantilevers were doped with POCl3(1020cm3). 2μm-thick cantilevers were fabricated onto PSG(2μm-thick). Sublimation drying method was used at releasing step to avoid stiction. Then, the device was vacuum sealed. Device was fixed to a sodalime-glass#1 with silver paste and it was wire bonded. Glass#1 has a predefined hole and a sputtered silicon-film at backside. The front-side of the device was sealed with a sodalime-glass#2 using the glass frit. After getter insertion via the hole, backside of the glass#1 was sealed electrostatically with a sodalime-glass#3 at 10-6 torr. After sealing, getter was activated. Sealing was successful to operate the tunneling device. The packaged VMFS showed reduced emission current compared with the chamber test prior to sealing. The emission currents were changed when the magnetic field was induced. A VMFS of angular anodes were tested and its sensitivity was about 3%.
In conventional IR-sensors, there are problems of needing cooler and sensing wavelength limitation. These problems can be achieved by using un-cooling thermal IR senors. However, they raise the problems of the attack of pyroelectric thin film layer during the etching of sacrificial layer as well as the thermal isolation of the IR detection layer. In order to fabricate uncooled IR-sensor using pyroelectric film, multilayer should be prepared pyroelectric thin film and thermally isolating membrane structure of square-shaped microstructures. We used the direct bonding technique to avoid the thermal loss by silicon substrate and the attack of pyroelectric thin film by etchant of the sacrificial layer. Metallic Pt layer used as a top and a bottom electrodes were deposited by E-beam sputtering method, while pyroelectric thin films were prepared Sol-Gel techniques. Because the pyroelectric thin film with c-axial orientation raised thermal polarization without the polling, the more integrated capability could be achieved. We investigated the characterized of the pyroelectric thin films: P-E loop, dielectric constant, XRD etc.
This work reports a direct bonding method between silicon wafers using an interlayer. Thermal oxide, sputtered silicon nitride, molybdenum film and electron-beam evaporated silicon oxide were used as an interlayer. Silicon wafers were hydrophilized by one of the host nitric acid, the sulfuric acid based solution and the ammonium hydroxide based solution, mated at class 100 hemisphere and heat treated. After hydrophilization of silicon wafers, the changes of the surface roughness' were studied by the atomic force microscopy and the voids and the non-bonded areas were inspected by the infra-red transmission microscope. The bonding interfaces of the bonded pairs were inspected by a high resolution scanning electron microscope. Surface energies and tensile strengths of the bonded pairs were also tested by the crack propagation method and the push-pull meter, respectively. Surface energy of the Si-Si wafer pair annealed at 150 degree(s)C for 48 hours was about 7200 [erg/cm2] and its tensile strength was more than 18 MPa. This tensile strength is comparable with the bulk strength of the used silicon wafer.