RECORDING HEAD TECHNOLOGY BASIC

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RECORDING HEAD TECHNOLOGY BASIC

• School of Mechanical Engineering
• Institute of Engineering
• Suranaree University of Technology

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Outline

• Magnetic and Magnetism
• History of Magnetic Recording
• Digital Data Encoding and Decoding
• HDD Write Head Technology
• HDD Read Head and MR Technology
• HDD Recording Material
• Introduction to Head Fabrications
• Introduction to HDD Head Test

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HDD Component
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HDD Recording Head
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Magnetism

• Magnetism is one of the phenomena by which
  materials exert an attractive or repulsive forces
  on other materials.
• Some well known materials that exhibit easily
  detectable magnetic properties are nickel, iron,
  some steels, and the mineral magnetite.

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Magnetism

• The ancient Greeks, originally those near the
  city of Magnesia, and also the early Chinese knew
  about strange and rare stones with the power to
  attract iron.
• Chinese found that a steel needle stroked with
  such a "lodestone" became "magnetic" when freely
  suspended, pointed north-south.    
• Around 1600 William Gilbert, proposed an
  explanation the Earth itself was a giant magnet,
  with its magnetic poles some distance away from
  its geographic ones

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Lodestone
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Magnetism

• Until 1821, only one kind of magnetism was known,
  the one produced by iron magnets.
• Hans Christian Oersted noticed that the current
  caused a nearby compass needle to move.
• Andre-Marie Ampere, who concluded that the nature
  of magnetism was quite different from what
  everyone had believed.
• It was basically a force between electric
  currents two parallel currents in the same
  direction attract, in opposite directions repel.

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Magnetic Dipoles

• Normally, magnetic fields are seen as dipoles,
  having a "South pole" and a "North pole"
• A magnetic field contains energy, and physical
  systems stabilize into the configuration with the
  lowest energy.
• The magnetic energy, so-called flux flows from
  the north pole to the south pole.

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Magnetic Dipoles

• Magnetic dipoles result on the atomic scale from
  the two kinds of movement of electrons.
• First the orbital motion of the electron around
  the nucleus.
• Second source of electronic magnetic moment is
  due to a quantum mechanical property called the
  spin dipole magnetic moment

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Magnetic Field
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Type of Magnet

• Permanent Magnets
• Electromagnets

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Permanent magnets

• A few elements -- especially iron, cobalt, and
  nickel -- are ferromagnetic at room temperature.
• Every ferromagnetic has its own individual
  temperature, called the Curie temperature, or
  Curie point,
• A long bar magnet has a north pole at one end and
  a south pole at the other. Near either end the
  magnetic field falls off inversely with the
  square of the distance from that pole.
• For a magnet of any shape, at distances large
  compared to its size, the strength of the
  magnetic field falls off inversely with the cube
  of the distance from the magnet's centre.

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Classification of Magnetic Materials

• Diamagnetism
• Paramagnetism
• Ferromagnetism
• Antiferromagnetism
• Ferrimagnetism

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Diamagnetism

• In a diamagnetic material the atoms have no net
  magnetic moment when there is no applied field.
• Under the applied field (H) the spinning
  electrons produces a magnetisation (M) in the
  opposite direction to that of the applied field

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Paramagnetism

• In paramagnetism materials each atom has a
  magnetic moment which is randomly oriented as a
  result of thermal agitation.
• The magnetic field creates a slight alignment of
  these moments and hence a low magnetisation in
  the same direction as the applied field.

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Ferromagnetism

• Ferromagnetism is only possible when atoms are
  arranged in a lattice and the atomic magnetic
  moments can interact to align parallel to each
  other.
• Only Fe, Co and Ni are ferromagnetic at and above
  room temperature

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Antiferromagnetism

• Antiferromagnetic materials are very similar to
  ferromagnetic materials but the exchange
  interaction between neighboring atoms leads to
  the anti-parallel alignment of the atomic
  magnetic moments.

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Ferrimagnetism

• Ferrimagnetism is only observed in compounds,
  which have more complex crystal structures than
  pure elements

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Classification of Magnetic Materials
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Electromagnet

• An electromagnet is a wire that has been coiled
  into one or more loops, known as a solenoid.
• When electric current flows through the wire, a
  magnetic field is generated.
• The more loops of wire, the greater the
  cross-section of each loop, and the greater the
  current passing through the wire, the stronger
  the field.
• Uses for electromagnets include particle
  accelerators, electric motors, etc

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The Orientation of Magnet

• The orientation of this effective magnet is
  determined via the right hand rule.

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Magnetic Phenomena

• An electric current produces a magnetic field.
• Some materials are easily magnetized when placed
  in a weak magnetic field. When the field is
  turned off, the material rapidly demagnetizes.
  These are called "Soft Magnetic Materials."

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Magnetic Phenomena

• In some magnetically soft materials the
  electrical resistance changes when the material
  is magnetized. The resistance goes back to its
  original value when the magnetizing field is
  turned off. This is called "Magneto-Resistance"
  or the MR Effect.
• Certain other materials are magnetized with
  difficulty but once magnetized, they retain their
  magnetization when the field is turned off. These
  are called "Hard Magnetic Materials" or
  "Permanent Magnets."

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HISTORY OF MAGNETIC RECORDERS

• In 1888, Oberlin Smith originated the idea of
  using permanent magnetic impressions to record
  sounds.
• In 1900, Vladeniar Poulsen demonstrated a
  Telegraphone. It was a device that recorded
  sounds onto a steel wire.
• Although everyone thought it was a great idea,
  they didn't think it would succeed since you had
  to use an earphone to hear what was recorded.

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HISTORY OF MAGNETIC RECORDERS

• Until 1935, all magnetic recording was on steel
  wire.
• Then, at the 1935 German Annual Radio Exposition
  in Berlin, Fritz Pfleumer demonstrated his
  Magnetophone. It used a cellulose acetate tape
  coated with soft iron powder.
• The Magnetophone and its "paper" tapes were used
  until 1947 when the 3M Company introduced the
  first plastic-based magnetic tape.

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HISTORY OF MAGNETIC RECORDERS

• In 1956, IBM introduced the next major
  contribution to magnetic recording - the hard
  disk drive. The disk was a 24-inch solid metal
  platter and stored 4.4 megabytes of information.
• Later, in 1963, IBM reduced the platter size and
  introduced a 14-inch hard disk drive.

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HISTORY OF MAGNETIC RECORDERS

• In 1971, 3M Company introduced the first 1/4-inch
  magnetic tape cartridge and tape drive.
• In that same year, IBM invented the 8-inch floppy
  disk and disk drive. It used a flexible 8-inch
  platter of the same material as magnetic tape.
• In 1980, a little-known company named Seagate
  Technology invented the 5-1/4-inch floppy disk
  drive.

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PREREQUISITES FOR MAGNETIC RECORDING

• Input Signal
• Recording Medium
• Magnetic Head

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Input Signal

• An input signal can come from a microphone, a
  radio receiver, electrical device, or any other
  source that's capable of producing a recordable
  signal.
• Some input signals can be recorded immediately,
  but some must be processed first.
• This processing is needed when an input signal is
  weak, or is out of the Frequency response range
  of the recorder.

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Recording Medium

• A recording medium is any material that has the
  ability to become magnetized, in varying amounts,
  in small sections along its entire length.
• Some examples of this are magnetic tape and
  magnetic disks

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Magnetic Heads

• Magnetic heads are the transducers that convert
  the electrical input signal into the magnetic
  that are stored on a recording medium.
• Magnetic heads do 3 different things.
• Transfer signal onto the recording medium.
• Recover signal from the recording medium.
• Remove signal off the recording medium.

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Writing Magnetic Data
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Reading Magnetic Data
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Integrating the Write/Read Heads
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HDD Data Encode and Decode

• Digital information is a stream of ones and
  zeros.
• Hard disks store information in the form of
  magnetic pulses.
• In order for the PC's data to be stored on the
  hard disk, therefore, it must be converted to
  magnetic information.
• When it is read from the disk, it must be
  converted back to digital information.

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HDD Data Encode and Decode

• Magnetic information on the disk consists of a
  stream of very small magnetic fields.
• Information is stored on the hard disk by
  encoding information into a series of magnetic
  fields.
• This is done by placing the magnetic fields in
  one of two polarities either N-S, or S-N

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HDD Data Encode and Decode

• Although it is conceptually simple to match "0
  and 1" digital information to N-S and S-N
  magnetic fields.
• The reality is much more complex a 1-to-1
  correspondence is not possible, and special
  techniques must be employed to ensure that the
  data is written and read correctly.

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Technical Requirements

• Fields vs. Reversals
• Synchronization
• Field Separation

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Fields vs. Reversals

• Read/write heads are designed not to measure the
  actual polarity of the magnetic fields, but
  rather flux reversals.
• Flux reversals occur when the head moves from an
  area that has N-S polarity to S-N, or vice-versa.

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Fields vs. Reversals

• The reason the heads are designed based on flux
  reversals instead of absolute magnetic field, is
  that reversals are easier to measure.
• The encoding of data must be done based on flux
  reversals, and not the contents of the individual
  fields.

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Synchronization

• Another consideration in the encoding of data is
  the necessity of using some sort of method of
  indicating where one bit ends and another begins.
  
• Even if we could use one polarity to represent a
  "one" and another to represent a "zero", what
  would happen if we needed to encode on the disk a
  stream of 1,000 consecutive zeros?

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Field Separation

• Although we can conceptually think of putting
  1000 tiny N-S pole magnets in a row one after the
  other. They are additive.
• Aligning 1000 small magnetic fields near each
  other would create one large magnetic field, 1000
  times the size and strength of the individual
  components.

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Data Encoding

• We must encode using flux reversals, not absolute
  fields.
• We must keep the number of consecutive fields of
  same polarity to a minimum.
• To keep track of which bit is where, some sort of
  clock synchronization must be added to the
  encoding sequence.

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Data Encoding
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Media Limitation

• Each linear inch of space on a track can only
  store so many flux reversals.
• We need to use some flux reversals to provide
  clock synchronization, these are not available
  for data.
• A prime goal of data encoding methods is
  therefore to decrease the number of flux
  reversals used for clocking relative to the
  number used for real data.

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Media Limitation

• Over time, better methods that used fewer flux
  reversals to encode the same amount of
  information.
• Hardware technology strives to allow more bits to
  be stored in the same area by allowing more flux
  reversals per linear inch of track.
• Encoding methods strive to allow more bits to be
  stored by allowing more bits to be encoded (on
  average) per flux reversal.

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Data Encode/Decode Methods

• Frequency Modulation (FM)
• Modified Frequency Modulation (MFM)
• Run Length Limited (RLL)
• Partial Response, Maximum Likelihood (PRML)
• Extended PRML (EPRML)

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Frequency Modulation (FM)

• This is a simple scheme, where a one is recorded
  as two consecutive flux reversals, and a zero is
  recorded as a flux reversal followed by no flux
  reversal.
• This can also be thought of as follows a flux
  reversal is made at the start of each bit to
  represent the clock, and then an additional
  reversal is added in the middle of each bit for a
  one, while the additional reversal is omitted for
  a zero.

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FM
Bit Pattern Encoding Pattern Flux Reversals Per Bit Bit Pattern Commonality In Random Bit Stream
0 RN 1 50
1 RR 2 50
Weighted Average Weighted Average 1.5 100
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FM

• The name "frequency modulation" comes from the
  fact that the number of reversals is doubled for
  ones compared to that for zeros.
• A byte of zeroes would be encoded as
  "RNRNRNRNRN",
• A byte of all ones would be "RRRRRRR
• The ones have double the frequency of reversals
  compared to the zeros hence frequency modulation
  (meaning, changing frequency based on data value).

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FM

• FM is very wasteful
• Each bit requires two flux reversal positions,
  with a flux reversal being added for clocking
  every bit.
• Compared to more advanced encoding methods that
  try to reduce the number of clocking reversals,
  FM requires double (or more) the number of
  reversals for the same amount of data.

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Modified Frequency Modulation

• MFM improves on FM by reducing the number of flux
  reversals inserted just for the clock.
• Instead of inserting a clock reversal at the
  start of every bit, one is inserted only between
  consecutive zeros.
• When a 1 is involved there is already a reversal
  (in the middle of the bit) so additional clocking
  reversals are not needed.
• When a zero is preceded by a 1, we similarly know
  there was recently a reversal and another is not
  needed. Only long strings of zeros have to be
  "broken up" by adding clocking reversals.

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MFM
Bit Pattern Encoding Pattern Flux Reversals Per Bit Bit Pattern Commonality In Random Bit Stream
0 (preceded by 0) RN 1 25
0 (preceded by 1) NN 0 25
1 NR 1 50
Weighted Average Weighted Average 0.75 100
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MFM

• Since the average number of reversals per bit is
  half that of FM, the clock frequency of the
  encoding pattern can be doubled, allowing for
  approximately double the storage capacity of FM.

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MFM

• MFM encoding was used on the earliest hard disks,
  and also on floppy disks.
• Since the MFM method about doubles the capacity
  of floppy disks compared to earlier FM ones,
  these disks were called "double density".
• In fact, MFM is still the standard that is used
  for floppy disks today.
• For hard disks it was replaced by the more
  efficient RLL methods.

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Run Length Limited

• An improvement on the MFM encoding is Run Length
  Limited or RLL.
• This is a more sophisticated coding technique, or
  more correctly stated, "family" of techniques.
• RLL is a family of techniques because there are
  two primary parameters that define how RLL works,
  and therefore, there are several different
  variations.

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RLL

• RLL takes MFM technique one step further.
• It considers groups of several bits instead of
  encoding one bit at a time.
• The idea is to mix clock and data flux reversals
  to allow for even denser packing of encoded data,
  to improve efficiency.
• The two parameters that define RLL are the run
  length and the run limit (and hence the name).

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RLL

• The word "run" here refers to a sequence of
  spaces in the output data stream without flux
  reversals.
• The run length is the minimum spacing between
  flux reversals, and the run limit is the maximum
  spacing between them.
• As mentioned before, the amount of time between
  reversals cannot be too large or the read head
  can get out of sync and lose track of which bit
  is where.

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RLL

• The particular variety of RLL used on a drive is
  expressed as "RLL (X,Y)" or "X,Y RLL"
• X is the run length and Y is the run limit.
• The most commonly used types of RLL in hard
  drives are "RLL (1,7)", and "RLL (2,7)"
• Consider the spacing of potential flux reversals
  in the encoded magnetic stream. In the case of
  "2,7", this means that the smallest number of
  "spaces" between flux reversals is 2, and the
  largest number is 7.

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RLL
Bit Pattern Encoding Pattern Flux Reversals Per Bit Bit Pattern Commonality In Random Bit Stream
11 RNNN 1/2 25
10 NRNN 1/2 25
011 NNRNNN 1/3 12.5
010 RNNRNN 2/3 12.5
000 NNNRNN 1/3 12.5
0010 NNRNNRNN 2/4 6.25
0011 NNNNRNNN 1/4 6.25
Weighted Average Weighted Average 0.4635 100
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RLL

• If we were writing the byte "10001111" (8Fh),
  this would be matched as "10-0011-11" and encoded
  as "NRNN-NNNNRNNN-RNNN".
• Since every pattern above ends in "NN", the
  minimum distance between reversals is two.
• The maximum distance would be achieved with
  consecutive "0011" patterns, resulting in
  "NNNNRNNN-NNNNRNNN" or seven non-reversals
  between reversals. Thus, RLL (2,7).

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RLL
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Peak Detection

• Standard read circuits work by detecting flux
  reversals and interpreting them based on the
  encoding method.
• The controller converts the signal to digital
  information by analyzing, synchronized to
  internal clock, and looking for small voltage
  spikes in the signal that represent flux
  reversals.
• This traditional method of reading and
  interpreting hard disk data is called peak
  detection.

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Peak Detection

• The circuitry scans the data read from the disk
  looking for positive or negative "spikes" that
  represent flux reversals.

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Peak Detection

• This method works fine as long as the peaks are
  large enough to be picked out from the background
  noise of the signal.
• As data density increases, the flux reversals are
  packed more tightly and the signal becomes much
  more difficult to analyze.
• This can potentially cause bits to be misread
  from the disk.

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Peak Detection

• To take the next step up in density, the magnetic
  fields must be made weaker.
• This reduces interference, but causes peak
  detection to be much more difficult.
• At some point it becomes very hard for the
  circuitry to actually tell where the flux
  reversals are.

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PRML

• To combat this problem a new method was
  developed.
• This technology, called partial response, maximum
  likelihood or PRML, changes entirely the way that
  the signal is read and decoded from the surface
  of the disk.

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PRML

• PRML employs sophisticated digital signal
  sampling, processing and detection algorithms to
• Manipulate the analog data stream coming from the
  disk (the "partial response" component)
• Determine the most likely sequence of bits this
  represents ("maximum likelihood")

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PRML
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Extended PRML (EPRML)

• An evolutionary improvement on the PRML is
  extended partial response, maximum likelihood, or
  EPRML.
• This advance was the result of engineers tweaking
  the basic PRML design to improve its performance.
  
• EPRML devices work in a similar way to PRML.
• They just use better algorithms and
  signal-processing circuits.

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EPRML

• The chief benefit of using EPRML is that due to
  its higher performance, areal density can be
  increased without increasing the error rate.
  Claims regarding this increase range from around
  20 to as much as 70, compared to "regular"
  PRML.
• EPRML has now been widely adopted in the hard
  disk industry and is replacing PRML on new drives.

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Recording Head Technology
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Recording Head Technologies

• Ferrite Heads
• Metal-In-Gap (MIG) Heads
• Thin Film (TF) Heads
• (Anisotropic) Magnetoresistive (MR/AMR) Heads
• Giant Magnetoresistive (GMR) Heads
• Colossal Magnetoresistive (CMR) Heads
• TMR Heads

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Ferrite Heads

• The oldest head design is also the simplest
  conceptually.
• When writing, the current in the coil creates a
  polarized magnetic field in the gap between the
  poles of the core, which magnetizes the platter.
• When the direction of the current is reversed,
  the opposite polarity magnetic field is created.
• For reading, the process is reversed.

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Ferrite Heads
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Metal-In-Gap Heads

• The improvement of ferrite head design was
  Metal-In-Gap heads.
• They are essentially the same design, but add a
  special metallic alloy in the head.
• This change greatly increases its magnetization
  capabilities, allowing MIG heads to be used with
  higher density media.
• They are usually found in PC hard disks of about
  50 MB to 100 MB.

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Thin Film Head

• Thin Film (TF) heads--also called thin film
  inductive (TFI)--are a totally different design
  from ferrite or MIG heads.
• They are so named because of how they are
  manufactured.
• TF heads are made using a photolithographic
  process similar to how processors are made.

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Thin Film Head

• Thin film heads are capable of being used on much
  higher-density drives and with much smaller
  floating heights.
• They were used in many PC HDD in the late 1980s
  to mid 1990s, usually up to 1000 MB capacity
  range.

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Thin Film Head Structure

• A thin film head structure consists of 20
  material layers with patterns for each layer
  defined by photolithography and either additive
  processing (electroplating, liftoff masking) or
  subtractive processing (ion milling, wet etching,
  reactive ion etching, chemical mechanical
  processing).

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Thin Film Head Structure
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Critical Thin Film Head Features

• Two critical features in the thin film head, the
  width of the read sensor (MRw) and the width of
  the write pole tip (P2w), determine areal density
  performance.
• The lithography techniques for the MR sensor are
  comparable to gate requirements in integrated
  circuits. The lithography processing for the
  write pole tip can be compared with the
  interconnect processing strategy in the
  integrated circuit.

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AMR Head

• The newest type of technology commonly used in
  read/write heads is much more of a radical change
  to the way the read/write head works.
• While conventional ferrite or thin film heads
  work on the basis of inducing a current in the
  wire of the read head in the presence of a
  magnetic field, magnetoresistive (MR) heads use a
  different principle entirely to read the disk.

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AMR Head

• An MR head employs a special conductive material
  that changes its resistance in the presence of a
  magnetic field.
• As the head passes over the surface of the disk,
  this material changes resistance as the magnetic
  fields change corresponding to the stored
  patterns on the disk.

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AMR Head

• The MR head is not generating a current directly
  the way standard heads do, it is several times
  more sensitive to magnetic flux changes in the
  media.
• This allows the use of weaker written signals,
  which lets the bits be spaced closer together
  without interfering with each other, improving
  capacity by a large amount.

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AMR Head

• MR technology is used for reading the disk only.
  For writing, a separate standard thin-film head
  is used.
• This splitting of chores into one head for
  reading and another for writing has additional
  advantages.
• Traditional heads that do both reading and
  writing are an exercise in tradeoffs, because
  many of the improvements that would make the head
  read more efficiently would make it write less
  efficiently, and vice-versa.

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AMR Head

• First introduced in 1991 by IBM but not used
  widely until several years later, MR heads were
  one of the key inventions that led to the
  creation of hard disks over 1 GB.
• Despite the increased cost of MR heads, they have
  now totally replaced thin film heads.

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AMR Head

• Even MR heads however have a limit in terms of
  how much areal density they can handle.
• The successor to MR is GMR heads, named for the
  giant magnetoresistive effect.
• They are similar in basic concept to MR heads but
  are more advanced

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GMR Head

• First discovered in the late 1980s by two
  European researchers, Peter Gruenberg and Albert
  Fert, who were working independently.
• Working with large magnetic fields and thin
  layers of various magnetic materials, they
  noticed very large resistance changes when these
  materials were subjected to magnetic fields.

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GMR Head

• IBM developed GMR into a commercial product by
  experimenting with thousands of different
  materials and methods.
• A key advance was the discovery that the GMR
  effect would work on multilayers of materials
  deposited by sputtering.
• By December 1997, IBM had introduced its first
  hard disk product using GMR heads.

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GMR Head Technology
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Evolution of R/W Head
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Giant magnetoresistive effect

• Giant Magnetoresistance (GMR) is a quantum
  mechanical effect observed in thin film
  structures composed of alternating ferromagnetic
  and nonmagnetic metal layers.
• The effect manifests itself as a significant
  decrease in resistance to a lower level of
  resistance when sensing different magnetic field.

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GMR Technology

• The spin of the electrons of the nonmagnetic
  metal align parallel or antiparallel with an
  applied magnetic field in equal numbers, and
  therefore suffer less magnetic scattering when
  the magnetizations of the ferromagnetic layers
  are parallel.

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GMR
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Types of GMR

• Multilayer GMR
• Granular GMR
• Spin valve GMR

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Multilayer GMR

• Two or more ferromagnetic layers are separated by
  a very thin (about 1 nm) non-ferromagnetic spacer
  (e.g. Fe/Cr/Fe).
• The GMR effect was first observed in the
  multilayer configuration, with much early
  research into GMR focusing on multilayer stacks
  of 10 or more layers.

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Granular GMR

• Granular GMR is an effect that occurs in solid
  precipitates of a magnetic material in a
  non-magnetic matrix.
• In practice, granular GMR is only observed in
  matrices of copper containing cobalt granules.
• Granular GMR materials have not been able to
  produce the high GMR ratios found in the
  multilayer counterparts.

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Spin valve GMR

• Two ferromagnetic layers are separated by a thin
  (about 3 nm) non-ferromagnetic spacer.
• If the coercive fields of the two ferromagnetic
  electrodes are different it is possible to switch
  them independently.
• Therefore, parallel and anti-parallel alignment
  can be achieved, and normally the resistance is
  again higher in the anti-parallel case. This
  device is sometimes also called spin-valve.
• Spin-valve GMR is the configuration that is most
  industrially useful, and is the configuration
  used in hard drives.

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Spin valve GMR

• When the head passes over a magnetic field of one
  polarity (say, "0"), the free layer electrons
  turn to be aligned with those of the pinned
  layer this creates a lower resistance in the
  entire head structure.

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Spin valve GMR

• When the head passes over a magnetic field of the
  opposite polarity ("1"), the electrons in the
  free layer rotate so that they are not aligned
  with those of the pinned layer. This causes an
  increase in the resistance of the overall
  structure.

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GMR head materials

• Free Layer
• Spacer
• Pinned Layer
• Exchange Layer

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Free Layer

• This is the sensing layer, made of a nickel-iron
  alloy, and is passed over the surface of the data
  bits to be read.

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Spacer

• This layer is nonmagnetic, typically made from
  copper, and is placed between the free and pinned
  layers to separate them magnetically.

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Pinned Layer

• This layer of cobalt material is held in a fixed
  magnetic orientation by virtue of its adjacency
  to the exchange layer.

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Exchange Layer

• This layer is made of an "antiferromagnetic"
  material, typically constructed from iron and
  manganese, and fixes the pinned layer's magnetic
  orientation.

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AMR VS GMR

• AMR heads typically exhibit a resistance change
  of about 2, for GMR heads this is anywhere from
  5 to 8.
• GMR heads can detect much weaker and smaller
  signals, which is increasing areal density,
  capacity and performance.
• GMR are much less subject to noise and
  interference because of their increased
  sensitivity, and they can be made smaller and
  lighter than MR heads

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TMR Phenomena

• The magneto resistance in a tunnel-valve
  originates from a change in tunneling probability
  dependent on the relative magnetic orientation of
  two ferromagnetic layers.
• The response of a free ferromagnetic layer to the
  magnetic field of the storage media results in a
  change of electrical resistance in the
  tunnel-valve sensor.

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TMR
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Spin-Valve VS Tunnel Valve
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TMR Read Head
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Perpendicular Recording

• One of the key challenges facing the hard drive
  industry is overcoming the constraints imposed by
  the superparamagnetic effect.
• Which occurs when the microscopic magnetic grains
  on the disk become so tiny that ambient
  temperature can reverse their magnetic
  orientations.
• The result is that the bit is erased and, thus,
  data is lost.

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Perpendicular Recording
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PMR Platter Structure
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PMR Response
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Today PMR HDD

• 2006 Seagate the world's first 3.5 inch Cheetah
  15K 300GB storage.
• 2006 Toshiba 40GB MK4007GAL 1.8 HDD
• 2006 Fujitsu 160GB MHW2160BH 2.5" HDD
• 2006 Seagate Barracuda 7200.10, 750 GB 3.5 HDD.
• 2007 Hitachi announced the first 1 Terabyte Hard
  Drive

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PMR HDD
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HDD HEAD Fabrications
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Wafer fabrication processes

• Wafer is the common word of raw material for ICs
  manufacturing. Usually thin, round and silicon
  crystal in diameter 150, 200 and 300 mm. The
  wafer fabrication is normally operated under
  vacuum and cleanroom.
• Preparation of wafer media
• Wafer processing

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Preparation of wafer media

• Wafer media is fabricated as substrate of next
  processes.
• Crystal growth and wafer slicing
• Thickness sorting
• Lapping etching
• Thickness flatness checking
• Polishing
• Final Testing

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Wafer processing

• Photolithography
• Additive processing
• Thin film technology
• Subtractive processing
• Wet etching
• Dry etching (Ion milling, Plasma etching,
  Reactive ion etching)
• Modifying (dopant)
• Diffusion
• Ion implantation

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Wafer
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Basic of head slider fabrication

• Slider fabrication is the process of parting
  wafer containing thousands of recording heads
  into a form factor called slider.
• Each slider embodying one recording head.
• The flying height of less that 10 nm has mandated
  the use of the most advanced micromachining and
  vacuum technologies to deliver the extreme
  mechanical sophistications required in the
  sliders.

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Basic of head slider fabrication
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Basic of head slider fabrication
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Fly Height?
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Basic of head slider fabrication

• Thin and polish wafer by lapping
• Bonded the entire wafer to a platform
• Wafer slicing into row of slider by multi-blade
• The rows are processed in various ways, including
  lapping and ion milling to form air bearing
  surface (ABS)
• Dividing to each slide

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Basic of head slider fabrication
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Basic of head slider fabrication
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HGA - HSA
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Basic of media fabrication
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Glass substrate

• highly planar
• low defect
• Smoothness
• Suit modulus which yields stable mechanical
  properties in the drive

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Glass substrate fabrication

• Design of Glass Composition
• Glass Melting and Molding
• Machining Brittle Materials
• Precision Cleaning

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Glass Substrates Manufacturing
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Magnetic Media

• Under layer Cr
• Magnetic layer CoPtCrB
• Antiferromagnetic layer Ru
• Can be fabricated by decomposition techniques
  such as sputtering
• The Ruthenium layer is about 3 atom-thick layer

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QA