Roger Jeffery

Investigation of Cerium-Substituted Europium Iron Garnets Deposited by Biased Target Ion Beam Deposition

We report on the deposition, crystallization, and magnetic properties of cerium-substituted europium iron garnet having the general form of (CeEu)₃(FeGa)₅O₁₂. The films were deposited on gallium gadolinium garnet and fused quartz substrates using biased target ion beam deposition at a rate of 2.7 nm/min. The Ce:EIG thin film has a composition of Ce_1.3Eu_1.7Fe₃Ga_1.6O₁₂, with 30% of the Ce in the 4+ oxidation state and the remainder as Ce³⁺. The film exhibits the primary peaks of the garnet phase in X-ray diffraction patterns. In the visible part of the electromagnetic spectrum, the film on GGG exhibits a Faraday rotation of 3.3°/μm with coercivity of 0.58 kOe, whereas the film on fused quartz exhibits 1.1°/μm with a coercivity of 0.8 kOe. The film on the fused quartz substrate has a saturation magnetization of 17 emu/cm³ at room temperature.

Preparation and Characterization of Cerium Substituted Bismuth Dysprosium Iron Garnets for Magneto-Optic Applications

We report on cerium substituted bismuth dysprosium iron garnet of composition Bi1.3Ce0.3Dy1Fe5O12 prepared by biased target ion beam deposition on a fused quartz substrate and postdeposition crystallization through rapid thermal annealing in air. The resulting thin film garnet achieved promising magnetic and magneto-optic (MO) properties on a low cost amorphous substrate and with reduced thermal budget toward potential MO applications and semiconductor processing for films of similar composition.

Control of Sidewall Profile in Dry Plasma Etching of Polyimide

Spin-on polyimide is an organic thin film often used as a sacrificial layer for surface micromachining due to its high thermal stability, ease of removal, and compatibility with many materials and processes used in the realization of microelectromechanical systems (MEMS). The incorporation of sloped sidewalls in polyimide for fabricating pedestal structures is crucial in order to provide strong anchors in free-standing MEMS devices, especially in cases having a high aspect ratio and/or where structural materials have limited deposition conformality. This paper demonstrates a reliable reactive ion etching (RIE) methodology for tuning the polyimide sidewall angle, ranging from a vertical sidewall up to an angle of about 25° from the vertical. The key modifications to the process parameter space include changes to the process temperature and chamber pressure. This paper also presents a novel lift-off process, which is based on the use of an interfacial polymer layer to facilitate removal of an overlying silicon oxide hard mask. This procedure allows polyimide sacrificial layers employing a silicon oxide hard mask to be used on samples that have exposed silicon oxide layers elsewhere on the chip that are required to remain intact during hard mask removal. Therefore, this lift-off process is applicable in situations where the silicon oxide hard mask removal cannot be accomplished by wet etching in hydrofluoric acid solutions. [2016-0314]

Control of chemical composition of rare-earth substituted iron garnets using biased target deposition

Rare earth cerium substituted europium iron garnets (CeEu)3(FeGa)5O12 (Ce:EIG) as well as the elemental oxides were deposited on fused quartz substrates using Biased Target Deposition (BTD). The Ce:EIG films are prepared at low temperature (80-120°C) by sputtering four metallic targets simultaneously using a low energy ion beam. This method provides control over the material composition in a predictable way by controlling the bias duty cycle on individual targets.

Issues in source calibration for biased target ion beam deposition

We report issues associated with the calibration of a biased target ion beam deposition system. Variations in deposition rates and oxygen flow have been observed when depositing individual metal oxide films immediately after films deposited from different targets as compared to depositions following films from the same target.

Low temperature through-wafer reactive ion etching for MEMS

This paper presents the results of experimental work on a low temperature through-wafer reactive ion etching (RIE) technique obtained in the course of development of a process that can be used in small sample processing for microelectromechanical systems (MEMS). Low temperature RIE are a crucial step for many dry MEMS fabrication processes, where can be used to fabricate silicon vias, trenches, and to perform dry release of membranes and other devices. The through-wafer etch developed here can be used also to separate fabricated devices, especially when it is desirable to produce non-rectangular shapes, which cannot be cut using a dicing saw. The presented process works with large silicon wafers as well as with small samples. In this work we developed a method which allows for stabilization of the sample temperature at the correct level during the entire process, which allows through wafer etch of thick silicon samples. The results obtained indicate that there is no universal process suited to all applications. Here we present three different recipes suitable for various applications.

Capturing the impulse response of a second order system

The impulse response of a system is of great significance when analysing a systems properties. Due to the short time scales involved in some cases, capturing this transient response requires a high degree of timing accuracy. This paper discusses the techniques used in designing a data acquisition system for initiating and recording the impulse response of a second order system. Consisting of an ADC, input buffer, FPGA, and GUI, the system can be used to analyse a range of system responses on nanosecond time scales.

Plasma annealing as an effective method for the crystallization of bismuth iron garnet films

Oxygen plasma annealing was used to crystallise (BiDy)₃(FeGa)₅O₁₂ (Bi:DyIG) at a temperature of 515°C, which is over 100°C lower compared with conventional thermal annealing. We used a thermal imager to measure and characterise the temperature of the sample with respect to RF power and pressure inside a plasma chamber.