W.W. Clegg

ACTIVE VIBRATION CONTROL AND ACTUATION OF A SMALL CANTILEVER FOR APPLICATIONS IN SCANNING PROBE INSTRUMENTS

Abstract The deflection control of a small cantilever is described, which operates using a single active piezoelectric element and optical vibration sensing, so that unwanted vibrations in the cantilever are removed, and yet it remains possible to deflect the cantilever statically or dynamically as required. Such a control system is directly applicable to the very small cantilevers found in scanning probe microscopes, such as atomic force and magnetic force microscopes, the resolution of which is limited by unwanted vibration.

Feasibility of ultra-dense spin-tunneling random access memory

Three-dimensional (3-D) finite element models have been utilized to simulate electromagnetic behaviors in spin-tunneling random access memory (STram). The most significant contributors have been identified. Compared with conventional current-in-plane (CIP) giant magneto-resistive (GMR) memory, whose signal level is inversely proportional to the square root of the storage density, these current-perpendicular-to-plane (CPP) STram elements provide an excellent readout property in that their signal level is independent of their cross-section area. This result is so attractive that the density of STram should not be limited by signal degradation. Moreover, a magnetic flux closure design was found to reduce the crossfeed by about a factor of five, compared with conventional keeperless design, which is the most favored approach for achieving 10/sup 9/ bits/cm/sup 2/ areal density. Although the storage mechanism described in this paper is made of STram, the flux-closure design could be generally applicable to other magnetic solid state memories.

The preparation of piezoceramic–polymer thick films and their application as micromechanical actuators

Abstract There is currently considerable interest in the development of piezoelectric materials with properties that cannot at present be attained with single-phase materials. Composite piezoelectric thick films have been prepared and characterized. These films, deposited directly onto metallized glass cantilevers, have been shown to be effective as micro-actuators.

Development of a scanning laser microscope for magneto-optic studies of thin magnetic films

Abstract A magneto-optic scanning laser microscope has been built which is capable of observing the magnetic domain structure present in materials which exhibit the Kerr (polar and longitudinal) and Faraday magneto-optical effects. The samples are not specially coated to improve the Kerr contrast, images being formed of the domain structures in the “as produced” samples. The instrument is also capable of observing nonmagnetic contrast. In addition the microscope may be used, together with a high-power Ar ion laser, as a thermo-magneto-optic bit writer

Head-disk spacing variation suppression via active flying height control

A novel active flying height control method is proposed for the suppression of head-disk spacing variation in hard disk drives under shock or vibration conditions. The thermal signal detection method is used for real-time derivation of the spacing variation signal for feedback control. Design details of the servo control system are given. Simulation results are provided to demonstrate the effectiveness of the method.

Polarization interferometer for measuring small displacement

A homodyne polarization laser interferometer is presented for high-speed measurement of small displacements. No modulation technique is used, so the opto-mechanical setup is relatively simple. The dual-beam arrangement enables the displacement to be measured while the use of polarization interferometry enables the determination of the directional nature of the displacement. Another feature of this interferometer lies in the fact that it is also suitable for the measurement of head-media spacing of a hard disk drive. Combined with the electronics used at present, sub-nanometer resolution is achievable. Its measurement bandwidth is limited only by the sampling rate of the A/D board being used.

Measurement of the modal shapes of inhomogeneous cantilevers using optical beam deflection

The study of free vibrations of systems such as simple cantilevers has been mainly concerned with the determination of the eigenvalues (frequencies) and eigenfunctions (modal shapes). A technique has been developed, using optical beam deflection, to measure the modal shape of a cantilever non-invasively at each modal frequency. A knowledge of the modal shapes of very small cantilevers incorporating suitable actuators is important in the application of active vibration control to micromechanical structures.

A DIFFERENTIAL INTERFEROMETER FOR SCANNING FORCE MICROSCOPY

A magnetic force instrument is described which makes use of a differential interferometer which can be used with a very short length cantilever in the force detection assembly. Conventional methods work with cantilevers of a few millimetres in length, but are not suitable for the very much smaller commercial cantilevers which are now available. The instrument described contains novel features which enable it to be used with such cantilevers. Topographical images of calibration specimens and magnetic images of hard disk samples obtained using this instrument are presented.

PZT thin film Bi-layer devices for phase controlled actuation in MEMS

A potential application for ferroelectric thin films is micro positioning and actuation. For using PZT films as micro-actuators it is desirable to have film thicknesses of comparable size to the underlying structure. The amount of actuation possible is determined by a number of factors: the piezoelectric coefficient d31, geometric factors and the compliance of both the actuator and cantilever and the electric field across the film. Using a bi-layer should therefore increase the amount of actuation for a given drive voltage. Bi-layer devices can also be driven at constant voltage, and their actuation varied by the phase difference of the drive voltage between the two layers. PZT films of thickness 0.5 μm have been deposited as a bi-layer. Micro-actuators have been fabricated using these structures, their electric properties measured and their electro-mechanical properties characterised and evaluated using optical beam deflection.

Observations of magneto‐optic phase contrast using a scanning laser microscope

A scanning laser microscope (SLM) has been built which is capable of observing magnetic structure via ‘‘conventional’’ Kerr imaging techniques and a ‘‘novel’’ magneto‐optic phase contrast approach. This latter contrast mode highlights magnetic transitions, rather than domains themselves. In this paper we present results of observations in TbFeCo samples using this phase contrast technique and assess its possible application as a read‐out mechanism for magneto‐optic recording systems.