Shu Y. Wu

Memory retention and switching behavior of metal-ferroelectric-semiconductor transistors

The memory retention and switching behavior of a metal-ferroelectric-semiconductor transistor using bismuth titanate have been investigated. The study made on p-channel transistors shows that the device has a fast switching speed and a switching threshold at a field of about 15 to 20 kV/cm. It also has a good memory retentivity. The low current OFF state is more stable than the high current ON state. The current in the ON state was found to decay logarithmically with time at long elapsed times. This is attributed to a slow trapping of holes at the ferroelectric-semiconductor interface states.

Optical switching characteristics of epitaxial bismuth titanate films for matrix-addressed displays

Abstract Electro-optic switching properties of (010) epitaxial Bi4Ti3O12 films grown on (110) MgAl2O4 substrates have been investigated. The measurements were carried out on large-area films in situ on the spinel substrate using an inter-digitated electrode array. A contrast ratio higher than 7:1 was obtained. Switching times of less than 5 μsec were measured at fields >60 kV/cm. Due to substrate clamping the field needed for switching the epitaxial film was about seven times higher than that for bulk single crystal at a same switching speed. The films exhibit an apparent switching threshold and grey scale capability. Finally, an experimental X-Y matrix-addressed display has been designed and evaluated.

Domain structure and polarization reversal in films of ferroelectric bismuth titanate

A preliminary study has been made of the structure, optical properties and polarization reversal behavior of epitaxial bismuth titanate films grown by sputtering on MgO substrates. As grown, the films are twinned on a coarse scale, with alternate regions oriented with the monoclinic (100) and (010) plane parallel to the (110) MgO surface. Optical birefringence measurements on these regions yielded Δna and Δnb values as a function of temperature which were in general agreement with those measured for bulk crystals. By annealing film sections detached from the substrate, a single orientation of the type (010) was obtained, and regions of such samples could be poled to a single-domain condition. Hysteresis data, with the field applied along the a and c axes, for single domain regions yielded spontaneous polarization results comparable to those reported previously for bulk crystals, but indicated somewhat higher coercive fields. Similar measurements with the field along the [101] axis showed that it is possib...

Electro‐optic contrast observations in single‐domain epitaxial films of bismuth titanate

Electro‐optic switching has successfully been demonstrated on untwinned (010) epitaxial bismuth titanate films grown on (110) MgAl2O4 substrates. This result is achieved on large‐area films using an interdigitated electrode array structure which can be used both for electrical poling and subsequent electro‐optic address. A contrast ratio higher than 7:1 between the on and off states is obtained with a 10‐μm‐thick film. A gradual variation of the contrast ratio with switching field is observed, which gives the film a capability for grey scale.

Optimization of epitaxial quality in sputtered films of ferroelectric bismuth titanate

Earlier phases of this study demonstrated the feasibility of growing epitaxial films of Bi 4 Ti 3 O 12 by rf sputtering from ceramic targets containing excess Bi 2 O 3 . These films were unsuitable for device exploitation of the unusual electro-optic display properties of bulk crystals of the titanate because of their twinned, multidomain character. During the present phase, clamping effects exerted by the MgO substrate were shown to prevent conversion by electrical poling to the single domain state. Other substrates were investigated, TiO 2 and sapphire giving the (001) orientation desired for the differential retardation display mode, and MgAl 2 O 4 giving the (010) orientation required for the extinction mode. The latter is obtained untwinned, a result attributed to the thermal expansion and lattice mismatch properties of the system, which, however, also lead to cracking and peeling due to large stresses along the film c -axis. The peeling problem was alleviated by a novel stress compensation growth technique resulting in films on MgAl 2 O 4 , showing minimal substrate clamping effects, and good electro-optic switching properties.

Transient switching response and partial switching phenomena in coarse-grained rhombohedral-phase PLZT ceramics

Abstract Transient switching response and partial switching phenomena in coarse-grained rhombohedral-phase lead-lanthanum-zirconate-titanate X/65/35, 7 ≤ X ≤ 8 (PLZT) ceramics have been investigated using the longitudinal electro-optic scattering effect. The measurements on the transient switching response and partial switching were made by sensing the optical contrast change, resulting from either the 180° polarization switching or the incomplete reversal of polarization, respectively. The results show that the ceramics exhibit a switching threshold, possess grey scale capabilities, and would suffer no cross-talk problems under pulsed switching. They would appear to possess good potential for X-Y matrix-addressed displays.