Can Mobile Phones damage GMR Heads by
Electromagnetic Interference (EMI)? Vladimir Kraz
Credence Technologies, Inc.Soquel, CA
vladimir@ credencetech.com
Al Wallash and Caleb ChangQuantum Corporation
Milpitas, CA al.wallash@ quantum.com ; caleb.chang@ quantum.com
2April 2000
Outline•Background•Purpose•Test Methodology•Experimental
•EMI sources and measurement equipment
•Introduction to Mobile Phones•Results•Summary
3April 2000
Background•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.
4April 2000
Purpose
•To study the effects of mobile phones in the proximity of the GMR heads during handling and testing•magnetic or resistance damage to GMR
sensor?•EMI induced changes to testers?
•Spin stand during dynamic electrical test (DET)•Quasi Static tester (QST)
5April 2000
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 effects.
6April 2000
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
7April 2000
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
8April 2000
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
9April 2000
TDMA Mobile Telephones
•Time Domain Multiplex Access•Transmits digitized voice in packets in
controlled time intervals •Typical duration of the transmission packet is
577µS 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 1800/1900MHz.
10April 2000
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.).
11April 2000
Thermal Balance of GMR HeadEnergy from EM field enters the GMR head via induction of voltage and currents and exits by •Convection: not a major contributor here.•Radiation: not a major contributor in our case.•Conduction: heat escapes GMR head sensor via surrounding shields and leads.
Power (energy / time) of the incoming energy is the most important factor in mechanism of melting of GMR head.
Convection
RadiationCo
nd
uc
tive Pa
th
Internal Reaction
Energy from ESD
•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.
12April 2000
Test A: Stand-Alone GMR HGA
Meas urement antenna( connected to
)os c illos cope
Fixture for HGA( )no HGA s hown
Signal injector terminals( )common mode and differential
Phone
ESD EventMonitor
( )Antenna loop
RF coax cable toos c illos cope
13April 2000
Test Results: Stand-Alone GMR HGA
& Mobile Phones
:No antenna connected
• No damage
11 Teles copic Antenna cm 30and cm
( ): no phone s hown
• No damage
Single loop antenna150mm( ):previous s lide
• No damage
70 Double loop mm antenna: connected
• No damage
14April 2000
Test Results: Stand-Alone GMR HGA & ESD Sources
Single loop 150mm antenna
•RF Bag: No damage
•Tube w/cylinders: Head open
Double loop 70mm(not shown)
•RF Bag: Head open
Telescopic monopole 11cm antenna
•RF Bag: No damage
•Tube w/cylinders: No Damage
Telescopic monopole 30cm antenna
•RF Bag: No damage
•Tube w/cylinders: Head open
15April 2000
Source Assessment 9362 (1.5 ) 001 LeCroy GHz os cillos cope with a CTS antenna
~ 3".Dis tance between the s ource and the antenna was21-Mar-0015 35 01
2 ns 20.0mV 49.9mV
2 ns
20 mV 10 GS/s
21-Mar-0015 37 04
.5 s 20.0mV 13.4mV
.5 s
20 mV 100 MS/s
21-Mar-0015 27 28
10 ns 200mV 1.090 V
10 ns
.2 V 10 GS/s
21-Mar-0015 30 12
.1 s 200mV -378mV
.1 s
.2 V 500 MS/s
21-Mar-0015 31 28
20 ns 200mV -378mV
20 ns
.2 V 2.5 GS/s
AMPS Phone 1.33V/m CDMA Phone 0.345V/m TDMA Phone 3.48V/m
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.
16April 2000
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
17April 2000
Test C: GMR HGA in Guzik Tester
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 exposure
18April 2000
Test Results: GMR HGA & Guzik Tester
Damage Assessment
Mobile Phones•No damage to the
head
ESD Events•No damage to the
head
Other ArtifactsAMPS and CDMA
phones•None
ESD Events•None
TDMA phone•Error in tester
(see next slide)
19April 2000
DET Testing
Changes during stability (COV) testing by •ESD Generator (rod)•TDMA cell phone
LF TAA (mV) TAAA (%) COV (TAA) (%) Asym_write
Initial 1 0.96 13.75 1.04 2.62Initial 2 0.97 12.71 0.74 2.37
After AMPS phone 0.96 14.30 0.96 2.46AMPS during test 0.96 13.03 0.89 2.82CDMA during test 0.97 14.18 0.93 2.66After ESD bag 0.96 13.79 0.91 2.57ESD bag during test 0.96 13.65 0.89 2.76After ESD rod 0.96 14.50 0.99 2.44
ESD rod during test 0.97 13.11 1.57 56.58TDMA during test 0.96 13.08 1.26 3.99
20April 2000
Test Results: GMR HGA & Guzik Tester with TDMA cell phone
Error 2034 during DET testing caused by TDMA cell phone
21April 2000
Summary of Test Results
:All types No damage
: All mode ls No damage
: :TDMA phone Tes ter error
" 2034: Error Signal Uns table "during main gain adjus tment
GMR HGA mounted on Guzik tes ter
/ :Plas tic bag w connectors
-- .Fatal damage open : All mode ls No damage 2.75" GMR HGA with double loop antenna
(70 ) mm diameter
/ :Plas tic bag w connectors
No damage
/ :Plas tic rod w cylinders
-- .Fatal damage open
: All mode ls No damage 6" GMR HGA with s ingle loop antenna(150 ) mm diameter
:All types No damage
: All mode ls No damage GMR HGA mounted on QST
/ :Plas tic bag w connectors
-- .Fatal damage open : All mode ls No damage 30 GMR HGA with cm monopole antenna
connected to one end
:All types No damage
: All mode ls No damage 11 GMR HGA with cm monopole antenna connected to one end
:All types No damage
: All mode ls No damage GMR HGA with no antenna connected
ESD SourcesMobile PhonesTest Setup
22April 2000
Conclusion• 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
Top Related