Invited Paper
From Perpendicular Magnetic Recording to Heat Assisted Magnetic Recording 2 l l 3 3 Kai-Zhong Gao , Xiaobin Wang , Tim Rausch , Alexander Wu , Yukiko Kubota , Timothy 3 l l l 3 3 Klemmer , Chubing Peng , Yingguo Peng , Darren Karns , Xiaobin Zhu , Yinfeng Ding , Eric KC 3 l l 3 3 l Chang , Yongjun Zhao , Hua Zhou , Hassib Amini , Jan-Ulrich Thiele , Mike Seigler , Ganping 3 l 4 3 2 4 Ju , Edward Gage , Charles Henr , Cynthia Hipwell I, Steve Hwang , John Dykes and Mark Re
Abstract- Heat (HAMR)
is
Assisted
considered
Magnetic
as
one
of
Recording the
leading
density limit close to 1Tb/in
2
for a given SNR
criterion estimated for HDD application at that
technology candidates for enabling continuous areal
time [4]. The primary limitation is due to so called
density growth to beyond perpendicular magnetic
write-ability-thermal
recording (PMR) and increase the storage capacity of
which triggers the perpendicular media design and
the hard disk drives. In this paper, we give a brief
development
review of the technology development over the past decade, from PMR to the current progress in HAMR
on
stability-SNR tilted
tri-lemma,
anisotropy
medium,
exchange coupled composite structure, exchange
from various perspectives and show how HAMR can
spring medium and gradient anisotropy system [5-
extend areal density growth beyond PMR. We will
9].
also
look
into
technology
and
the
fundamental
show
the
aspects
challenges
of HDD
for
Beyond
2 1Tb/in ,
a
new
break
through
is
beyond
required. Over the past 10 years, the HDD areal
Index Terms-Perpendicular magnetic recording,
density has rapidly approached the proposed limit 2 of lTb/in . While the primary focus has been to
current state ofHAMR technology.
heat
assisted
magnetic
recording,
switching
field
distribution, erasure
reduce the medium switching field vs. anisotropy (thermal stability for a given grain size), another learning
I.
shows
that
the
impact
of
medium
switching field distribution (SFD), defined as the
INTRODUCTION
Perpendicular magnetic recording (PMR) has
anisotropy distribution in PMR system, is the
been demonstrated as the alternative technology
primary limiting factor for PMR areal density
for
growth [4]. In other words, the PMR system was
continuous
areal
density
growth
beyond
longitudinal magnetic recording (LMR) over the
not limited by medium coercivity, but by medium
past decade [1-2]. The demonstration of PMR with
SFD due to finite write field gradient from the
an areal density exceeding LMR occurred in 2003,
recording
and
demagnetization fields are of the same order as
jump
started
the
HDD
industry
for
this
head.
Since
medium
SFD
and
technology transition with the first product launch
medium coercivity (Hc), this leads to performance
just a couple years after that demonstration point.
degradation due to erasure, which occurs before
All the HDD products were using PMR within a
thermal stability-trilemma in PMR system.
couple of years, with the highest areal density now more
than
5X compared
to
the
first
product
II.
HAMR technology demonstration
HAMR has been proposed for over two decades
launched using PMR. Previously, the detailed recording physics study
and over the past decade. Various companies in
suggested that conventional PMR could provide a
HDD industry have put a more focused study on
2X improvement in writeability, with potential
this technology [10]. In order to exceed the areal
additional
gains
from
density
orientation
ratio,
which
an a
improved total
areal
media density
limit
for
perpendicular
recording,
one
major challenge is to find an efficient path to
improvement over LMR of approximately 5X [3].
deliver
Earlier studies using recording physics model have
writing. To get to the resolution needed to exceed 2 1Tb/in , the optical and thermal spot size needs to
shown that conventional PMR will have an areal
energy
to
the
medium
surface
during
be far less than the typical diffraction limit set by Manuscript received 2 Oct., 2012 (date on which paper is submitted Technology
for
review).
LLC,
MN
Kaizhong 55435
Gao
is
(Phone:
the wavelength of the laser utilized. To achieve this
Seagate
goal, an efficient near field transducer (NFT) is
952-402-7743;
placed close to the magnetic write pole tip to help
with
email:
[email protected]). I. Seagate Recording Head R&D. 2. Seagate Twin City Operations 3. Seagate Recording Media R&D. 4. Seagate Media Head R&D.
FB-1
to define a thermal spot size to be much less than 100nm [11]. On the other hand, a high anisotropy
Invited Paper
medium with high SNR capability, such as FePt
The 1Tb/in
2
HAMR BTD has shown that the
composite, is required in order to achieve such
effective write field gradient, as defined by the
recording performance [12].
temperature dependent Hc gradient, is higher than aspects,
that of the conventional PMRsystem [14]. This
steady progress has been made in HAMR. A 2 I Tb/in areal density demonstration was recently
higher effective write field gradient offsets the
Despite
huge challenges in
various
performed that exceeded conventional PMR. addition,
a
functioning
HAMR
drive
increased medium SFD during the write process
In
[15]. The recording model also shows that if a high
was
thennal gradient can be obtained, the adjacent
demonstrated [11-13]. These demonstrations have
track
shown
conventional PMR[16].
a
strong
signal
on
a
new
technology
transition for the HDD industry. In
this
talk,
we
will
erasure may
be reduced as compare to
Despite recent rapid progress in both areal
review
these
HAMR
demonstrations. The initial demonstration clearly
density
and
drive
integration
using
HAMR
technology, there are still several unresolved issues
shows the impact of heating from NFT in the write
complicating
process [11]. A more recent base technology spin
HDDs. The major issues includes media switching
stand recording demonstration (BTD) of HAMR, 2 at l.007 Tbits/in with linear density of 1975 kBPI
magnetic
and track density of
sensitivity to head-to-media separation (HMS), and
510
kTPI,
resuled
from
its
integration
into
commercial
field distribution, alignment of the thennal and gradients,
NFT
protrusion,
high
advances in NFT heads and FePt media. Figure 1
[mally, the optical/thermal profile resolution limit.
shows the Log(bit error rate) bathtub curve for this 2 1. 007 Tbits/in BTD [12]]
All of these are complex and highly interrelated.
Log(BER)
Log(BER)
It is concluded that the realization of HAMR in commercial HDDs will require additional break through that solve these problems. However, once the
problems
are
identified,
the
solutions
are
usually not that far away.
With a recent full disk
demonstration
BPM
utilizing
recording,
we
anticipate the combination of both technologies can extend HDD well into the next decade. REFERENCES [I]
Y. Chen, X. Dang, et ai, IEEE Trans. Magn. 39, no. 5, 2368-70, Sept. 2003.
[2] OD
{(
Position Relative to Written Track (nm)
OTC:Onm RWO '" -70.72 nm LoglBERJ = ·1.99 Squeeze" 0 ZTP OTe Threshold =·2 Curve Fit" Quadratic
".-,:----;-;0=;;;; --,;;lD '" 1975.0 KBPI TO = 510.0 KTPI AD", 1007.3 Gb/inl
I
»
Toshiba
press
release
for
perpendicular
product
http://www.toshiba.co.jp/about/press/2004 12/pr140I.ht
ID
ill [3]
Data Rate" 833.9 Mbls RPM", 4200; Sectors" 16 Radius = 24.384 mm; Skew = 0.00· TO '" 510.0 KTPI; TP '" 49.8 nm Iw =61.0 mO. bp; Bias = 0.350 rnA Code: SID formatted
H. N. Bertram and M. Williams, IEEE Trans. Magn. 36, no. I, p. 4-9, Jan 2000.
[4]
K. Z. Gao and H. N. Bertram, IEEE Trans. Magn. 39, no. 2, 704 - 709, March 2003.
[S]
K. Z. Gao, O. Heinonen and Y. Chen, JMMM 321, Is 6,
[6]
K. Z. Gao and H. N. Bertram, IEEE Trans. Magn., 38 Is.
p.49S-S07, March 2009.
Figure 1 Seagate HAMR Demonstration from spin-stand 2 with an on track BER=E- at 1.007 Tbpsi (1975 kBPI x 510 kTPI)
6, p3675 - 3683, Dec. 2002. [7]
R. H. Victora and X. Shen, IEEE Trans. Magn. 41, Is. 2, pS37-42, Feb. 200S.
kBPI
=
777@698 MBPS
[8]
D. Suess, et ai, Appl. Phys. Lett., 87, Is 1, 012504, July 200S.
[9]
S Li, K Gao, L Wang, W Zhu, X Wang - US Patent 7,846,S64.
[10] M. H. Kryder et aI., Proceedings of the IEEE, 96, 1810 (2008). [11] w. A. Challener et aI., Nature Photonics, 3, 220 (2009). [12] A. Wu, et ai, TMRC 2012 Paper AI, to be published in IEEE Trans. Magn. 49, Jan 2013. [13] T. Rausch, J. D. Trantham, et ai, TMRC 2012 Paper B2, to be published in IEEE Trans. Magn. 49, Jan 2013. [14] X. Wang, K. Z. Gao, et ai, TMRC 2012 Paper AS, to be
Figure 2 an illustration of Seagate demonstration of an integrated HAMR drive. The sector BER was captured using an HAMR drive with an integrated head and FePt medium.
published in IEEE Trans. Magn. 49, Jan. 2013. [15] T. Rausch, J. A. Bain, D. Stancil, T. Schlesinger, IEEE Trans. Magn., 40, no. 1, 137-147, Jan. 2004. [16] K. Z. Gao, M. Williams et ai, IEEE Trans. Magn., 40, no. 4, 2449-24S1, July 2004. [17] David
III.
Kuo, et ai, TMRC paper F2, 2 SOOGd/in full disk demo.
Challenges for HAMR technology
FB-1
Seagate BPM
