CoPt Micromagnets by Electrodeposition

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1 CoPt Micromagnets by Electrodeposition Iulica Zana and Giovanni Zangari Dept. of Metallurgical and Materials Engineering and University of Alabama at Tuscaloosa This project was sponsored through DOD grant no. DAAH MINT Fall Review November 7, 2001

2 Outline Motivation permanent micromagnets for MEMS applications patterned media for magnetic recording Co-Pt as electroplated materials with high H c Co-Pt films: Structure and Magnetic Properties Fabrication and Properties of Micromagnets Summary and Outlook

3 Opportunities in MEMS Technology Permanent Magnet actuators are more versatile than electromagnetic actuators high force, large gaps zero-voltage operation but more difficult to fabricate Bi-directional actuation Permanent magnet µ-motors Integrated CMOS-PM processing: a breakthrough Bhansali et al J. MEMS 9, 245 (2000) 100 µm

4 Patterned Magnetic Media Conventional medium exchange coupling transition noise limit in bpi or thermal instability Patterned Medium + weak or no coupling + no transition noise + extend thermal stability limit complicated fabrication new signal processing, timing issues

5 Electrodeposition: : Process Advantages Similar lithography requirements to vacuum methods + Low cost and easy implementation + Better definition of element shape + Lower amount of defects at element walls + M switching strongly influenced by defects: better control of magnetic properties Limited materials set available Evaporation/Sputtering Electrodeposition

6 Permanent Magnet Films sputtered RE-TM: (BH) max = 480 kj/m 3 BUT only at low thickness CoNiMnP: (BH) max = 2.3 kj/m 3 ( µm 3 elements) Patterned Media by ECD: mostly pure metals (Co, Ni) by sputtering: pure metals, CoCrX or Co/Pt MLs Co 80 Pt 20 by ECD Materials Selection high anisotropy, high coercivity (H c up to 5.5 koe) hard magnetic properties observed in up to 10 µm thick films

7 Electrodeposition of Co Pt 20 Electrolyte: 10 mm Pt, 0.1 M Co as amino-citrate complexes, ph 8 Current Control, T = 65 C Cobalt counter-electrode No stirring µ-patterns defined by optical lithography (+) Co Ref (-) HOT PLATE

8 Epitaxy and Preferential Growth Crystal orientation and magnetic anisotropy are determined by: thin films: epitaxial relationships thick films: growth habit Epitaxy for in-plane anisotropy Si(110)/FCC(110)/BCC(112)/CoPt(1010) Epitaxy for out of plane anisotropy Si(hkl)/HCP(00.2)/CoPt(00.2) Si(hkl)/FCC(111)/CoPt(00.2) Growth habit: most often FCC(111) or HCP(00.2) In Plane Out of Plane

9 Co 80 Pt Films on Si(100)/Cu(100) Cu sputtered on H-Si: epitaxial growth according to Si(100)[011]//Cu(100)Cu(010) XRD spectrum taken after alignment using Si(400) quantitative comparison is possible Two orientations of Co-Pt are observed: CoPt(200) from increase in intensity of Cu(200) due to epitaxy CoPt FCC(111) or HCP(00.2) due to growth habit Epitaxial Growth? FCC or HCP?

10 TEM and SAD Small grain size (20-35 nm) FCC and HCP phases are present FCC(002) + (111) HCP(00.2) twinning FCC and HCP grains (from lack of registry of FCC and HCP reflections) 50 ma/cm2 Amount of HCP phase increases with current density Thanks to Dr. Shamsuzzoha 25 nm 10 ma/cm2

11 Co 80 Pt 20 /Cu: Magnetic Properties 20 /Si/Cu: Data not corrected for demag field Hc up to 2.5 koe in plane, 3.7 koe out of plane Squareness increases with thickness and current density (related to an increase in FCC(111)/HCP(00.2) intensity) Relevant perpendicular component of M

12 Co 80 Pt 20 4 x (Φ = 2 µm) 20 Patterns on Si(100)/Cu(100) 4 µm 4 µm High uniformity, regular walls and top surfaces

13 Micropatterns: : Magnetic Properties 1.0 // (933 Oe) (0.42) _ _ (1037 Oe) (0.19) 1.0 // (1828 Oe) (0.48) _ _ (3238 Oe) (0.40) 1.0 // (2047 Oe) (0.41) _ _ (3497 Oe) (0.46) Magnetization, (a.u.) Magnetization, (a.u.) Magnetization, (a.u.) Applied Field, (koe) Applied Field, (koe) Applied Field, (koe) 1/40 perpendicular In plane 1/20 2 µm 1/10 Increasing perpendicular remanence with increasing thickness, in agreement with crystallographic data

14 Micropatterns: Magnetic Properties 2 Loops corrected for demag field H c up to 3.7 koe at 220 nm

15 Permanent Magnet Performance (BH) max 35 kj/m 3 vs. 2.3 kj/m 3 of other groups Still far from bulk performance

16 Summary Fabrication of hard magnetic Co 80 Pt 20 films and µ-patterns by electrodeposition Films grow FCC + HCP On Cu(100), both epitaxial and growth-induced orientations are observed: CoPt(200)//Cu(200) CoPt FCC (111) and CoPt HCP (00.2) Small grain size, H c up to 3.7 koe Regular and uniform µ-patterns are obtained Perpendicular anisotropy increases with thickness

17 Outlook and Future Work Growth on epitaxial templates capable to stabilize HCP phase and single orientations, both in and out of plane Si(110)[001]//Cu(111)[110] Preliminary results Fabrication of sub-micron patterns (e-beam) for patterned media A unique, versatile material is available!