T.J.A. Popma

Plasma enhanced chemical vapor deposition silicon oxynitride optimized for application in integrated optics

Silicon Oxynitride (SiON) layers are grown from SiH4/N2, NH3 and N2O by Plasma Enhanced Chemical Vapor Deposition (PECVD). The process is optimized with respect to deposition of layers with excellent uniformity in the layer thickness (δd<1%), high homogeneity of the refractive index (Δn=2–7×10−4) and good reproducibility of the layer parameters. The optical losses of slab-type waveguides is determined to be as low as 0.2 dB/cm at 632.8 nm wavelength. Due to absorption of N–H and Si–H vibrational overtones, the optical losses in the third telecommunication window, around 1550 nm, is increased to about 2 dB/cm for low index layers. By an anneal step, however, the hydrogen content of the films can be reduced as is confirmed by IR-spectroscopy and the optical losses decrease to below 0.2 dB/cm. Based on the optimized PECVD SiON technology, a layer structure fulfilling the strong requirements of telecommunication devices, is designed for operation at 1550 nm wavelength. This structure, consisting of a SiON core layer (n=1.4857) surrounded by thick oxide cladding layers (n=1.4637), has the potential for realization of channel waveguides allowing for low-loss bends with a small bending radius and high fiber-to-chip coupling efficiency.

Optimization of a chemo-optical surface plasmon resonance based sensor

A surface plasmon based chemooptical sensor has been optimized by the use of computer simulation programs. Calculated and experimentally measured performances are in good agreement, showing the value of the simulation tool.

Thin-film ZnO as micromechanical actuator at low frequencies

A new model is proposed for the low-frequency piezoelectric activity of ZnO films grown on CVD SiO2. In this MOS structure, with ZnO as the semiconductor, a depletion layer is induced by means of a d.c. bias voltage. Using standard semiconductor theory, an expression is derived relating the electric field in this depletion layer with the driving a.c. and d.c. voltages. Due to the built-in charge at the ZnO-SiO2 interface, a depletion layer exists, even when no d.c. bias is applied. We measured the vibration amplitude at resonance of the tip of a silicon cantilever, upon which the MOS structure was deposited, as function of a.c. and d.c. voltages. The results show good agreement with calculated curves. Therefore, it can be concluded that thin-film ZnO can be used as a piezoelectric actuator for micromechanical devices working at low frequencies.

Reversal mechanism of submicron patterned CoNi/Pt multilayers

With laser interference lithography Co/sub 50/Ni/sub 50//Pt multilayers with perpendicular magnetic anisotropy have been patterned into regular matrices of submicron sized dots. Their magnetic properties have been studied with Vibrating Sample Magnetometry. Compared to continuous multilayers (H/sub c/=15 kA/m) the coercivity for the patterned multilayers is much larger (H/sub c/=115-270 kA/m). Though the hysteresis curves of 180 nm dots and 60 nm dots have identical shapes, virgin curves seem to indicate that the 180 nm dots are multidomain while the 60 nm dots are single domain. The latter has been confirmed with Magnetic Force Microscopy observations.

Optimization of LPCVD Silicon Oxynitride growth to large refractive index homogeneity and layer thickness uniformity

The thickness non-uniformity and refractive index in- homogeneity of silicon oxynitride thin films, grown by low pressure chemical vapor deposition, have been optimized. The present work was especially motivated by the application of these thin films as well defined waveguides in phase-matched second harmonic generating devices, which are well known for their extremely high requirements to uniformity and homogeneity. However, other demanding integrated optical components like gratings, sensor systems, telecommunication devices, etc., also strongly benefit from highly uniform waveguides.

Microstructure of Co-evaporated CoCr films with perpendicular anisotropy

Coevaporation of Co and Cr is applied to achieve good magnetic characteristics of media deposited at low temperature. The opposed oblique incidence vapor flux induces a columnar alignment parallel to the evaporation plane. Further, a process-induced segregation is present which introduces separated Co-rich and Cr-rich regions. A selective etching process is carried out to find proof of this. With increasing process temperature, nonelongated columns develop. The columnar axes are inclined towards the Co source at a smaller angle than the angle of incidence. The texture axes are also inclined, as are the anisotropy axes. The process-induced segregation results in an enhanced coercivity and saturation magnetization. A small in-plane anisotropy coincides with the direction of columnar alignment. At a higher process temperature, the column, texture, and anisotropy axis tilting decreases. >

A chromogenic crown ether as a sensing molecule in optical sensors for the detection of hard metal ions

A new chromogenic crown ether based on a merocyanine dye and a phenolic crown ether shows a striking selectivity for calcium or barium complexation and has a potential use in optical sensors.

Magnetic characterization of large area arrays of single and multi domain CoNi/Pt multilayer dots

Co50Ni50/Pt multilayers with perpendicular magnetic anisotropy have been patterned into single and multi domain dots by laser interference lithography and ion beam etching. The samples (typically 1×1 cm2) have been characterized by VSM, polar Kerr Magnetometry, Torque Magnetometry and Magnetic Force Microscopy. The relation between coercivity, anisotropy and dot size is discussed. Also the rotational hysteresis loss of single and multi domain dots is reported.

Transduction mechanisms and their applications in micromechanical devices

Transduction mechanisms and their applications in micromechanical actuators and resonating sensors are presented. They include piezoelectric, dielectric, electro-thermo-mechanic, opto-thermo-mechanic, and thermo-pneumatic mechanisms. Advantages and disadvantages with respect to technology and performance are discussed.<<ETX>>

Chromoionophores in optical ion sensors

The feasibility of surface plasmon resonance (SPR) for ion sensing has been investigated. Emphasis is laid on a simulation-based optimization of the SP carrying structure, as well as the applicability of a specific chemo—optical interface we have developed. A preliminary result is presented.