EE 666 Advanced Semiconductor Devices All About Hard Drives Lili Ji Lili Ji

EE666 Advanced Semiconductor Devices Outlines  Hard Drive History  Hard Drive Structures  Hard Drive Disk Media  Hard Drive Writing Heads  Hard Drive Reading Heads  Hard Drive Limits  What’s next?  Summary

EE666 Advanced Semiconductor Devices Hard Drive History  1956, IBM, RAMAC  5Mb Storage  50 disks, 24 inch in diameter

EE666 Advanced Semiconductor Devices Hard Drive History   First Modern Hard Disk Design (1973) IBM's model 3340, nicknamed the "Winchester", is introduced. With a capacity of 60 MB it introduces several key technologies that lead to it being considered by many the ancestor   First 3.5" Form Factor Disk Drive (1983) Rodime introduces the RO352, the first disk drive to use the 3.5" form factor, which became one of the most important industry standards   First Drive to use Magnetoresistive Heads (1990): IBM's model 681 (Redwing), an 857 MB drive.

EE666 Advanced Semiconductor Devices Hard Drive History

EE666 Advanced Semiconductor Devices Hard Drive Structures

EE666 Advanced Semiconductor Devices Hard Drive Disk Media  The gap between the head and the disk surface is about 15 nm.  Surface roughness should be a few nanometers.  Traditionally it is Al-Mg substrate with Ni-P on it. Now glass substrate is increasingly used.  Cr or Cr-V alloy are used as under layers to control the crystallographic orientation of the magnetic layer.  Co based alloy is used as the top magnetic layer,10~30nm in thickness.  Limited by grain size, areal density <35 Gb/sq.inch

EE666 Advanced Semiconductor Devices Hard Drive Disk Media Topography AFM picture RMS is about 8-12Å MFM image, dark and white Represents the bit information Sadamichi, Spin Dependent Transport in Magnetic Nanostructure

EE666 Advanced Semiconductor Devices Hard Drive Writing Head --- Longitudinal Writing Head S. Khizroev and D. Litvinov, J.A.P Vol 95,Num 9, May 2004

EE666 Advanced Semiconductor Devices Hard Disk Writing Head — Perpendicular Writing The first one use perpendicular is Toshiba’s mini hard drive MK8007GAH, which will be used in IPod, 80GB 1.8in S. Khizroev and D. Litvinov, J.A.P Vol 95,Num 9, May 2004

EE666 Advanced Semiconductor Devices Hard Drive Reading Heads ---AMR Reading Heads  Introduced by IBM in  ∆R/R=2~5%,providing areal density 1~5Gb/sq.inch  ∆Rcos 2 θ  R=R 0 + ∆Rcos 2 θ

EE666 Advanced Semiconductor Devices AMR Origin  Spin-Orbit coupling leads to spin dependent scattering of conduction electrons.(3d and 4s electrons)  3d orbitals will be affected by magnetization. They will mix and reorient, and show a larger scattering cross sections when electrons are moving parallel to M. And more scattering, or resistance!

EE666 Advanced Semiconductor Devices Hard Drive Reading Heads ---GMR Reading Heads  ∆R/R=10~50%, providing areal density larger than 10Gb/sq.inch

EE666 Advanced Semiconductor Devices GMR Origin  Spin-dependent transmission of carriers at interface between non-magnetic layer and magnetic layer.

EE666 Advanced Semiconductor Devices Hard Drive Bit Size

EE666 Advanced Semiconductor Devices Is there a limit? ----Yes…. Super Paramagnetic  Transmission Electron Micrograph of a Co-Cr-Pr-B magnetic media.  Fine grain size is around 85Å  Capable of supporting areal density 35Gb/sq.inch Sadamichi, Spin Dependent Transport in Magnetic Nanostructure

EE666 Advanced Semiconductor Devices What’s the problem?  Each bit usually contains hundreds of grains. Magnetic recording relies on the statistically averaging over those grains to get a satisfactory signal to noise ratio.  As bits size continue decrease, grain size need to be reduced, too. This can be achieved by under layer control.  However, eventually, the grains will become super paramagnetic.

EE666 Advanced Semiconductor Devices Super Paramagnetic  Definition: Magnetic information of the grain undergoes spontaneous switching by assistance of thermal energies. Magnetic information of the grain undergoes spontaneous switching by assistance of thermal energies.  Ms ----Saturation magnetization  Ku ---- Uniaxial anisotropy  V --- Volume of the grain  KuV---Magnetic anisotropy energy of the grain  To save information more than 10 years, KuV>40~50kT  As V decreasing, Ku need to be increased to avoid super paramagnetic!  Hc ----Switching field, Hc=2Ku/  0 Ms, so a larger field is needed to write information.

EE666 Advanced Semiconductor Devices Possible Solutions  Engineering media with narrower grain size distribution, so magnetic anisotropy Ku can be increased.  Perpendicular writing will have larger writing field, and supporting smaller bit size while at the same time allows more amount of grains in each bit.  Thermally assisted writing is to use laser to locally heat the media, to lower the coercivity Hc in that spot.

EE666 Advanced Semiconductor Devices What’s next? --- Patterned Magnetic Media  Bit size is decided by lithography.  Information is stored in a single domain magnet particle.  A 50 nm-period square dot array gives 250 Gb /sq.inch

EE666 Advanced Semiconductor Devices What’s Next? --BMR Reading Heads  Ballistic Magnetoresistive can provide a ∆R/R of more than 300%. Edward Price, CMRR& UCSD Physics.

EE666 Advanced Semiconductor Devices Summary  Smaller Bit Size +More sensitive reading heads  Larger Hard Drive!  Larger Hard Drive!  Now let's have some fun! Now let's have some fun! Now let's have some fun!