Mobile Phones _ GMR Heads – Bad Influence

Document Sample
Mobile Phones _ GMR Heads – Bad Influence Powered By Docstoc
					Can Mobile Phones damage
       GMR Heads by
Electromagnetic Interference
                Vladimir Kraz
          Credence Technologies, Inc.
                 Soquel, CA

          Al Wallash and Caleb Chang
             Quantum Corporation
                  Milpitas, CA ;
             • Background
             • Purpose
             • Test Methodology
             • Experimental
                • EMI sources and measurement equipment
             • Introduction to Mobile Phones
             • Results
             • Summary
April 2000                                                2
   • Electromagnetic interference (EMI) from a
         remote ESD-induced spark can damage
         GMR heads 1
             • No direct contact between ESD source and GMR head
             • Need close proximity, large voltage and extra wires
               connected to the GMR sensor
             • 500 V spark, 15 cm from GMR, 15 cm wire “antenna”
               connected to one GMR input
             • What about the EMI from other devices?
                • Cell phones, Walkie-Talkies, etc

   1. A. Wallash and D. Smith, “EMI Damage to GMR Heads”, Proc. 1998 EOS/ESD Symp.
April 2000                                                                           3
      • To study the effects of mobile phones in
             the proximity of the GMR heads during
             handling and testing
              • magnetic or resistance damage to GMR
             • EMI induced changes to testers?
                • Spin stand during dynamic electrical test (DET)
                • Quasi Static tester (QST)

April 2000                                                          4
                    Test Methodology
 • Step 1. Source Assessment
        • Identify mobile telephone technologies
        • Measure field strength and other properties of the
             electromagnetic fields generated by selected emission
             sources and controlled ESD events
 • Step 2. Exposure of GMR HGA to Emission
        • Expose GMR head to electromagnetic fields under
             controlled conditions and test for damage using QST
             tester. Expose HGA to emission from remote ESD
             events under the same circumstances. Compare the

April 2000                                                           5
                          EMI Sources
             RF Emission Sources
               • Motorola 845MHz CDMA phone
               • Nokia 6162 800 MHz TDMA phone
               • Motorola 830MHz AMPS phone

             ESD Sources
               • Plastic bag of SMA RF connectors
               • ESD Generator
                  • Plastic tube with two sliding metal cylinders
               • Barbecue lighter
                  • Spark produced by a piezoelectric crystal

April 2000                                                          6
             Measurement Equipment
   •LeCroy oscilloscope model 9362
   •HP Spectrum Analyzer model HP8595A
   •Credence Technologies' equipment
      • EMI/ESD Diagnostics Kit CTK053 with CTS001
        calibrated broadband active antenna
      • EM Eye CTM045 field strength meter
      • EM Aware ESD Event monitor CTC034 with local and
        remote antenna CTC113.
   •QST Tester model Integral Solutions International 2001
      • Resistance and amplitude measured
   •5 Gb/in2 PtMn GMR heads used in this study
          •30 VHBM magnetic failure level
April 2000                                                   7
                   Mobile Telephones
             1. Analog (AMPS)
              • Continuous transmission of signal in 800MHz band
              • Popular but obsolete

             2. TDMA
              • Time Domain Multiplex Access

             3. CDMA
              • Code Division Multiplex Access

April 2000                                                         8
             TDMA Mobile Telephones
        • Time Domain Multiplex Access
        • Transmits digitized voice in packets in
          controlled time intervals
        • Typical duration of the transmission packet is
          577S and the interval time is 4.6mS (GSM).
        • Variation: GSM is the most popular type of
          phones in the world. It is used almost
          exclusively in Europe and in many countries
          in Asia. TDMA phones work in two basic
          frequency bands -- 800/900 MHz and
April 2000                                                 9
             CDMA Mobile Telephones
      • Newest standard developed by Qualcomm
      • Relies on mathematical decoding of many
        signals coming to the receiver at the same time
        at the same frequency.
      • Each signal is spread over frequency using
        special type of encoding.
      • Tight control over the power of the signal: the
        farther away the phone is from the base station,
        the higher its transmission power.
      • They are popular in the U.S. and some countries
        in Asia (China, Korea, etc.).
April 2000                                             10
     Thermal Balance of GMR Head
 Energy from EM field enters the GMR head via
 induction of voltage and currents and exits by                                                                     n
 •Convection: not a major contributor here.
                                                                    Inte rnal Re action                          t
 •Radiation: not a major contributor in our case.      Ene rgy from ESD
 •Conduction: heat escapes GMR head sensor via
 surrounding shields and leads.                                                                            Radiation

 Power (energy / time) of the incoming energy is the

                                                                                            ctive P
 most important factor in mechanism of melting of

 GMR head.

 •Unlike ESD Events, emission from mobile phones and other EMI-related sources
 comes in on a continuous basis.

 •At some point, the temperature of GMR head assembly exposed to such radiation will
 reach equilibrium. If the sensor temperature reached at equilibrium is above the
 critical magnetic (~ 3000 C) or melting (~10000 C) temperatures, then the GMR sensor
 will be damaged.
April 2000                                                                                                              11
                Test A: Stand-Alone GMR
 RF coax cable to
     oscilloscope                          Measurement antenna
                                           (connected to
             ESD Event
               Monitor                          Fixture for HGA
                                                (no HGA shown)


                                          Antenna (loop)

                            Signal injector terminals
                            (common mode and differential)
April 2000                                                        12
             Test Results: Stand-Alone GMR
                    & Mobile Phones

             No antenna connected:
             •No damage
                                       Single loop antenna
             Telescopic Antenna 11cm   (previous slide):
             and 30cm                  •No damage
             (no phone shown):         Double loop 70mm antenna
             •No damage                connected:
                                       •No damage
April 2000                                                        13
             Test Results: Stand-Alone GMR
                  HGA & ESD Sources

        Single loop 150mm antenna
                                       Telescopic monopole 11cm antenna
        •RF Bag: No damage
                                       •RF Bag: No damage
        •Tube w/cylinders: Head open
                                       •Tube w/cylinders: No Damage
        Double loop 70mm
                                       Telescopic monopole 30cm antenna
        (not shown)
                                       •RF Bag: No damage
        •RF Bag: Head open
                                       •Tube w/cylinders: Head open
April 2000                                                                14
                             Source Assessment
                        LeCroy 9362 (1.5 GHz) oscilloscope with a CTS001 antenna
                         Distance between the source and the antenna was ~ 3".
             21-Mar-00                         21-Mar-00
             15 35 01                          15 37 04

              2 ns                              .5   s
              20.0mV                            20.0mV
               49.9mV                            13.4mV

             2 ns                              .5   s
              20 mV                             20 mV
                                     10 GS/s                        100 MS/s

             AMPS Phone 1.33V/m                CDMA Phone 0.345V/m             TDMA Phone 3.48V/m
             21-Mar-00                         21-Mar-00                       21-Mar-00
             15 27 28                          15 30 12                        15 31 28

              10 ns                             .1   s                          20 ns
              200mV                             200mV                           200mV
              1.090 V                            -378mV                          -378mV

             10 ns                             .1   s                          20 ns
              .2 V                              .2 V                            .2 V
                                     10 GS/s                        500 MS/s                            2.5 GS/s

         Bag with SMA: 7.18V/m                      Lighter: 10.05V/m                  Tube: 10.15V/m

       Strongest phone: TDMA. But still only ~ 30% of the field from ESD.
April 2000                                                                                                         15
             Test B: GMR HGA and QST

       All types of phones and all ESD sources were not
       able to generate any damage or upset the tester
April 2000                                                16
             Test C: GMR HGA in Guzik
  HGA was installed in the
  Guzik tester and was
  exposed to emission
  from mobile phones and
  ESD events before and
  during the test. A
  complete test was
  performed after each

April 2000                              17
        Test Results: GMR HGA & Guzik
      Damage                      Other Artifacts
       Assessment                 AMPS and CDMA
      Mobile Phones                phones
             • No damage to the     • None
              head                ESD Events
      ESD Events                    • None
             • No damage to the   TDMA phone
              head                  • Error in tester
                                      (see next slide)

April 2000                                               18
                              DET Testing
                       LF TAA (mV)   TAAA (%)   COV (TAA) (%)   Asym_write
Initial 1                 0.96        13.75         1.04           2.62
Initial 2                 0.97        12.71         0.74           2.37

After AMPS phone          0.96        14.30         0.96           2.46
AMPS during test          0.96        13.03         0.89           2.82
CDMA during test          0.97        14.18         0.93           2.66
After ESD bag             0.96        13.79         0.91           2.57
ESD bag during test       0.96        13.65         0.89           2.76
After ESD rod             0.96        14.50         0.99           2.44
ESD rod during test       0.97        13.11        1.57          56.58
TDMA during test          0.96        13.08        1.26           3.99

                   Changes during stability (COV) testing by
                     •ESD Generator (rod)
                     •TDMA cell phone
April 2000                                                                   19
         Test Results: GMR HGA & Guzik
           Tester with TDMA cell phone

       Error 2034 during DET testing caused by TDMA cell phone
April 2000                                                   20
               Summary of Test Results
       Test Setup                               Mobile Phones                  ESD Sources
       GMR HGA with no antenna connected        All models: No damage          All types:
                                                                               No damage

       GMR HGA with 11cm monopole antenna       All models: No damage          All types:
       connected to one end                                                    No damage

       GMR HGA with 30cm monopole antenna       All models: No damage          Plastic bag w/connectors:
       connected to one end                                                    Fatal damage -- open.
       GMR HGA mounted on QST                   All models: No damage          All types:
                                                                               No damage

       GMR HGA with single loop antenna 6"      All models: No damage          Plastic bag w/connectors:
       (150mm) diameter                                                        No damage
                                                                               Plastic rod w/cylinders:
                                                                               Fatal damage -- open.
       GMR HGA with double loop antenna 2.75"   All models: No damage          Plastic bag w/connectors:
       (70mm) diameter                                                         Fatal damage -- open.
       GMR HGA mounted on Guzik tester          All models: No damage          All types:
                                                TDMA phone: Tester error:      No damage
                                                "Error 2034: Signal Unstable
                                                during main gain adjustment"

April 2000                                                                                                 21
     • Under described test conditions mobile phones didn’t
             damage GMR heads
     •       Non-contact ESD Events were proved to be capable of
             introducing damage to GMR heads
     •       One type of mobile phone (TDMA) introduced errors
             during spin stand DET testing of GMR heads
     •       More testing needs to be done, especially with resonant
             circuits and in actual assembly and test conditions
     •       Though mobile phones so far didn’t prove to be
             damaging to GMR heads, it is still a good practice not to
             use them next to sensitive equipment because of other
             EMI-induced problems

April 2000                                                               22

Shared By: