Traugott Kallfass

A surface micromachined capacitive absolute pressure sensor array on a glass substrate

Abstract The fabrication process and the characteristics of a new surface micromachined pressure sensor array on a glass substrate are presented. The array consists of electrically parallel individual sensors with composite SiO 2 -Cr-SiO 2 diaphragms and vacuum-sealed cavities underneath. The cavities are created by lateral etching of an Al sacrificial layer. Capacitive sensing of pressure is accomplished via chromic electrodes. The performance of the sensor array is described. In a pressure range of 800 kPa a terminal-based nonlinearity less than 4% was measured for the arrays. The pressure sensitivity of the array is about 0.28 fF hPa −1 .

Matrix of light sensors addressed by a-Si:H TFTs on a flexible plastic substrate

A 2 inch matrix of 12288 light sensors was realized on a plastic substrate by low temperature thin film technology. In comparison to a glass realization the sensor matrix has a reduced weight, is unbreakable and flexible. Each sensor cell contains a photoconductor as a resistive sensor and a TFT for reading out the resistor values line by line. By using amorphous silicon for both the channel of the TFT and the photoconductor it is possible to fabricate the sensor matrix with a low number of masks. As gate insulator amorphous silicon nitride is used. The above mentioned films were deposited in a PECVD reactor in the same vacuum at 180 degree C which is suitable for PES-foils. The mismatch of the thermal expansion coefficients of the thin films and the plastic substrates causes peeling of the films and cracks. The remedy is the use of sputtered adhesion layers for the metallization and PECVD layers. To qualify the different adhesion layers a tape test method was used. Cracks were avoided by reducing the internal stress. For this reason a new layout was designed in which all PECVD layers are patterned in islands providing a minimum of internal stress. The TFTs show an ON/OFF ratio of 6 decades and a mobility of 0.3 cm2/Vs. The change of the a-Si:H conductivity under illumination is 6 nS/W/cm2. This value allows for a dynamic range of the sensor matrix of 60 dB. The new flexible sensor offers a wide variety of applications like an electronic eye with around view for the observation of wok pieces and traffic signs.

An array of TFT-addressed light sensors to detect grey shades and colours

An array of 12 288 pixels with light sensors in a-Si:H thin-film technology on a glass plate is described. An electronic circuit with a-Si:H-TFTs as switches in each pixel evaluates the grey shade of the light hitting the pixels. Colour filters allow detection of colours. The array of sensors is used to read video information such as drawings, pictures or documents with signatures without requiring optics. A lens in front of the array of cells enables it to detect distant objects.

Flexible and bistable FLC and cholesteric displays on plastic substrates for mobile applications and smart cards

Abstract— New smart-card applications like purse cards, etc. require an integrated display which allows the card-holder to read information which is stored on the IC of the card. On the other hand, the integration of a display into a plastic card requires some very specific features like flexibility and pressure stability, low-voltage CMOS-addressing, memory capability, and, of course, a reflective mode since no backlight is available. In this paper, two bistable reflective LCD solutions using ferroelectric and cholesteric LCs are discussed and very promising prototype results are presented. Pressure and bending tests as well as contrast measurements are compared in order to show the potential of meeting the requirements for use in smart cards.

17.2: A Backlight System Providing Variable Viewing Angles for Transmissive LCDs

A simple optical system is described which allows for the variation of the viewing angle of transmissive-type LCDs. It is well suited for automatic teller machines (ATMs) to switch between a wide viewing angle state which is defined by the used LCD and a restricted viewing angle for privacy, where a contrast of 30 at normal viewing direction decreases to a value of less than 0.3 at an angle of 30°.

Alignment layers for cholesteric displays on glass and plastic substrates

The optical performance of surface-stabilized cholesteric liquid-crystal displays (SCT-LCDs) has been optimized by using obliquely sputtered SiO 2 as the alignment layer. A comparison with polyimides used up to now showed an improvement in the contrast ratio by a factor of 2 for glass displays. A second advantage of this material is the absence of high temperatures during the manufacturing process. Therefore, it is possible to use obliquely sputtered SiO 2 for the preparation of plastic display prototypes. We have realized a 6-in. VGA display with approximately 130 dpi. This is the largest cholesteric display with the highest resolution fabricated on plastic substrates to date.

20.3,: A MIM-Addressed 16-in. EWS PDLC Display with Decreased Capacitance

We developed of a new fabrication process for MIMs to decrease the capacitance of the MIM. As a result of this the ratio CLC/CMIM is enlarged by a factor 5. The MIMs have a Ta2O5/Si3N4 double dielectric layer from which the Si3N4-layer is structured by a self-aligning backlighting process. With this process we achieved a very good homogeneity and a low defect rate of the MIM-elements. The improvement of the MIMs is demonstrated by a 16 inch MIM-addressed black and white EWS-PDLC-Display with 1280 × 1024 pixel sized 250μm × 250μm. To our knowledge this is the largest MIM-display also exhibiting the highest pixel density realized so far.

Highly linear capacitive pressure sensors with optimized electrode shapes

A method for linearizing a capacitive pressure sensor with a circular diaphragm by optimization of the electrode shapes is described. First a sensor with pressure dependent reference capacitor is used to linearize the ratio of the reference and the sensing capacitor. To improve the linearity furthermore a third pressure dependent capacitor in the sensor is added. An integrated CMOS amplifier using switched capacitor techniques is used to readout the sensor capacitors. Finally the measurement results of a thick-film sensor with a hybrid readout circuit are given.<<ETX>>

Thin film transistors for addressing LC-flat panel displays

Thin-film transistors (TFTs) are exceptionally qualified for addressing large-area liquid-crystal displays. The TFT circuits and the requirements for operating the picture elements in the displays are described. Further comments focus on the staggered structure of the TFTs and the materials a-Si:H and poly-CdSe used as semiconductors and Ta/sub 2/O/sub 5/, SiO/sub 2/, and SiN for gate isolators. The electrical data (such as mobility and off-current) of the TFTs determine the optical performance of the displays, characterized by a high contrast and a wide viewing angle.<<ETX>>