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