High performance hard magnetic NdFeB thick films for integration into micro-electro-mechanical systems

Abstract

Received PACS numbers: 75.50.Vv, 5µm thick NdFeB films have been sputtered onto 100 mm Si substrates using high rate sputtering (18 µm/h). Films were deposited at ≤ 500°C and then annealed at 750°C for 10 minutes. While films deposited at temperatures up to 450°C have equiaxed grains, the size of which decreases with increasing deposition temperature, the films deposited at 500°C have columnar grains. The out-of-plane remanent magnetization increases with deposition temperature, reaching a maximum value of 1.4 T, while the coercivity remains constant at about 1.6 T. The maximum energy product achieved (400 kJ/m 3 ) is comparable to that of high-quality NdFeB sintered magnets.NdFeB thin films with excellent hard magnetic properties have been prepared by sputtering 1 and Pulsed Laser Deposition. 2 Out-of-plane texture was induced by depositing the films onto heated substrates in both 1-step (directly crystallized) 1,2 and 2-step (crystallized during a post-deposition anneal) 3,4,5 processes. Thick films (≥5 µm) of such high performance hard magnetic materials have potential applications in magnetic MEMS (Micro Electro Mechanical Systems). 6 Their integration into MEMS requires the use of preparation techniques which can produce high deposition rates over large areas. In addition, the use of substrates which are compatible with today's MEMS technology (i.e. Si) is necessary for the exploitation of such materials. So far, the only group which has reported the successful growth of textured NdFeB thick films by high rate sputtering (≈30 µm/h) used metallic substrates. 3 in this letter, we report on the preparation and analysis of 5µm thick NdFeB films deposited on 100 mm Si substrates using high rate sputtering. The film's magnetic properties compare with those of high-quality sintered NdFeB magnets.{Ta (100 nm) / NdFeB(5 µm) / Ta (100 nm)} films were deposited onto (001) oriented Si substrates (diameter = 100 mm) at a rate of 18 µm/hour by triode sputtering of square targets of surface area 100 mm x 100 mm (note that the film thickness is reduced to 4 µm at the edge of the 100 mm wafer). The nominal composition of the NdFeB target was Nd 16.8 Fe 74.7 BB 8.5 .During deposition, the substrate was either "cold" (no power to substrate heater, though the substrate temperature gradually rises during deposition, eventually reaching a temperature of about 230°C) or fixed at a temperature in the range 300 -500°C. Full wafers were annealed at 750°C for 10 minutes. Structural characterization was carried out using high resolution Scanning Electron Microscopy (LEO Gemini 1530, equipped with In-Lens and Quadrant Back Scattering (QBSD) detectors as well as Energy Dispersive X-ray Analyzer (EDX)) andx-ray diffraction (Co radiation). For cross-sectional imaging, the samples were simply fractured while for plane-view imaging they were lightly polished to remove the Ta capping

Effect of laser beam parameters on magnetic properties of Nd–Fe–B thick-film magnets fabricated by pulsed laser deposition

“…Consequently, thick-film magnets have been extensively studied. [1][2][3][4] In addition to the magnetic properties of a film magnet; its deposition rate and the simplicity with which it can be incorporated in a machine are important factors in determining its usefulness. From the perspective of this latter factor, 5 we have studied rapid fabrication of isotropic Nd-Fe-B thick-film magnets by pulsed laser deposition (PLD).…”

Characterization of the magnetic properties of NdFeB thick films exposed to elevated temperatures

“…10 µm thick out-of-plane textured NdFeB hard magnet films were deposited using high rate triode sputtering 7 onto 525 µm thick Si substrates (diameter = 100 mm) thermally oxidized to a depth of 100nm. The room temperature values of remanence µ 0 M r and coercivity µ 0 H c were 1.2 T and 1.5 T, respectively.…”

“…[1][2][3][4][5][6][7] Triode sputtering is particularly well adapted to MEMS development, as very high sputtering rates can be achieved over large surface areas and thick textured films can be produced having magnetic properties comparable to those of sintered magnets. 2,7 Hard magnetic films may be exposed to elevated temperatures either in the course of fabrication (e.g. during thermomagnetic patterning (TMP) to produce multi-pole structures, 8 or during wafer bonding or device packaging steps) or during device use, and therefore it is important to know the thermal resistance of the magnetic film.…”

Micro-patterning of NdFeB and SmCo magnet films for integration into micro-electro-mechanical-systems

“…High rate triode sputtering has been shown to be suitable for the preparation of thick films of both SmCo 4 and NdFeB 5 alloys and we have recently used this technique to prepare high energy product 5 µm thick films of these materials on Si substrates (SmCo 7 -140 kJ/m 3 , NdFeB -400 kJ/m 3 ). 6,7 The second challenge to be solved is the lateral structuring of the films at the micron-scale.…”