Frode Tyholdt

A novel ultra-planar, long-stroke and low-voltage piezoelectric micromirror

A novel piston-type micromirror with a stroke of up to 20 µm at 20 V formed out of a silicon-on-insulator wafer with integrated piezoelectric actuators was designed, fabricated and characterized. The peak-to-valley planarity of a 2 mm diameter mirror was better than 15 nm, and tip-to-tip tilt upon actuation less than 30 nm. A resonance frequency of 9.8 kHz was measured. Analytical and finite element models were developed and compared to measurements. The design is based on a silicon-on-insulator wafer where the circular mirror is formed out of the handle silicon, thus forming a thick, highly rigid and ultra-planar mirror surface. The mirror plate is connected to a supporting frame through a membrane formed out of the device silicon layer. A piezoelectric actuator made of lead–zirconate–titanate (PZT) thin film is structured on top of the membrane, providing mirror deflection by deformation of the membrane. Two actuator designs were tested: one with a single ring and the other with a double ring providing bidirectional movement of the mirror. The fabricated mirrors were characterized by white light interferometry to determine the static and temporal response as well as mirror planarity.

The microwave dielectric properties of dual-layer PZT/ZrO2 thin films deposited by chemical solution deposition

The dielectric properties of dual-layer PZT/ZrO2 thin films were measured at microwave frequencies in both a metal?insulator?metal (MIM) capacitor and a coplanar waveguide (CPW) up to 50?GHz. Both PZT and ZrO2 films were prepared by the chemical solution deposition method. The measured dielectric loss of the PZT/ZrO2 film was approximately 0.08 at 30?GHz, much lower than that of typical PZT thin films. The dielectric constants obtained using the MIM capacitor with 360?nm PZT/65?nm ZrO2 and using the CPW with 420?nm PZT/280?nm ZrO2 were 47 and 130, respectively, at 50?GHz. Capacitance tunability was ~30% at +25?V and up to 50?GHz. The measured values obtained indicate that PZT/ZrO2 thin films may be suitable for the use of dielectric layers in tunable RF devices and RF MEMS capacitive switches operating at millimetre wave frequencies.

pMUT for high intensity focused ultrasound

Capacitive ultrasonic tranducers, cMUTs rely on the electrostatic field between the membrane and a back plate for sensing andactuation. This is an excellent solution for small amplitudes. But the movement of the membrane is physically limited by the bottom plate (risk of collapse). Furthermore, pull-in and linearity considerations restrict the available range to about one percent of thegap. Piezoelectric micromachined ultrasonic transducers, pMUTs, on the other hand have no such restrictions. The excitation is basedon lateral contraction of a thin film of Lead Zirconate Titanate, PZT, deposited on top of the membrane. Then there is no need for abackplate, and the linear range is greatly increased. Therefore, pMUTs are ideally suited for applications demanding large excitationamplitude, such as high intensity focused ultrasound, HIFU. In this work, we present pMUTs designed for HIFU operation around 1MHz.

Qualification and Applications of a Piezoelectric MEMS Process

An industrializable process for manufacturing of piezoelectric ultrasound transducer elements is demonstrated. The PZT film is deposited by chemical solution deposition on SOI wafers, and standard MEMS processes are utilized to make cantilevers, bridges and membranes. The PZT film of -50% of the devices exposed to thermal aging were found to fail at 85degC - 85%RH (relative humidity), while a real-life test of 8-1010 cycles at resonance only gives a slight change in Q-value and resonance frequency.