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2010 EOS/ESD Symposium
A Study on the Application of On-Chip EOS/ESD Full-Protection
Device for TMR Heads
Ray Nicanor M. Tag-at, Lloyd Henry LiHitachi Global Storage Technologies, Phil.
Corp.
Objectives
● To study and understand the different ESD
protection devices for TMR Heads.
● To have an effective ESD protection devices that
could enhance the robustness of the TMR heads.
Slide 2
Outline
● Introduction
● Experimental Setup
● Results
- I-V and R-V Characteristic Curves
- Shunt Diode’s Behavior
- Charging Mechanism of Diodes
- On-chip Diode Shunting Concept
● Conclusions
Slide 3
Outline
● Introduction
● Experimental Setup
● Results
- I-V and R-V Characteristic Curves
- Shunt Diode’s Behavior
- Charging Mechanism of Diodes
- On-chip Diode Shunting Concept
● Conclusions
Slide 4
Introduction
● Shunting is a commonly used method for on-chip ESD
protection.
● Diode can also work as a shunt across the TMR
sensor.
- Commonly installed across tester’s TMR input
terminals.
- Protects from electrical transients and EOS.
● There are already many published studies about
diode shunting in GMR/TMR heads.Slide 5
Introduction
What are the downsides of this method?
● Diodes can also be charged up through its
capacitance.
● TMR heads has no protection on the rest of the
assembly process.
Is it then possible to install shunt diodes into the device
itself?
Slide 6
Outline
● Introduction
● Experimental Setup
● Results
- I-V and R-V Characteristic Curves
- Shunt Diode’s Behavior
- Charging Mechanism of Diodes
- On-chip Diode Shunting Concept
● Conclusions
Slide 7
Experimental Set-up
● PSPICE Simulation
● Head Gimbal Assembly (HGA) Testers
- Quasi Static Tester (QST)
- Dynamic Electrical Tester (DET)
● Current Transients: Tek CT-6
● Input Signal Measurement: Tek P6248 Diff. Probe
● Diode: metal-to-silicon junction Schottky diode
D1N5711, Vth=0.3V
● HGAsSlide 8
Diode’s Characteristic
Slide 9
Diode’s capability to become conductive means
that it can be used as shunting device.
Depletion Region
● P-N semiconductor diode has
insulating region so-called the
“depletion region.”
● It becomes conductive in Forward Bias and
remains insulative at Reverse Bias.
p- doped
n-doped
● Depletion Region dictates the flow of current.
Outline
● Introduction
● Experimental Setup
● Results
- I-V and R-V Characteristic Curves
- Shunt Diode’s Behavior
- Charging Mechanism of Diodes
- On-chip Diode Shunting Concept
● Conclusions
Slide 10
Diode’s Characteristic Curves
I-V Curves
Slide 11
R-V Curves
● D1N5711 diode “Turn-on” voltage: 0.3 V
● Diode “on” Resistance, Rd: 300 ohms
● TMR Head’s nominal resistance: 500 ohms
Shunt Diode’s Behavior
Slide 12
● During Normal Testing and Operation
- PSPICE Simulation
• At lower operating frequency, the TMR input signal is the
same with and without diode.
• At higher frequency, the voltage across the TMR losses 3%
of it’s operating voltage when diodes are installed.
Slide 13
Shunt Diode’s Behavior
• TEK P6248 voltage differential probe
connected across the TMR’s input terminals.
• HGA Quasi Static Tester (QST) and Dynamic
Electrical Tester (DET) were used.
● During Normal Testing and Operation
- Actual Test Signal Measurements
Slide 14
Shunt Diode’s Behavior
- Results:
No Diode With Diode
HGA Quasi Test Parameters
HGA DET Test Signal
No difference in the Test Signal on with and without
shunt diodes!
Peak Voltage: 122 mV Peak Voltage: 122 mV
Slide 15
● During EOS/ESD Events
- PSPICE Simulation
Shunt Diode’s Behavior
• This simulates a HBM and MM ESD events during
testing or handling during fabrication and assembly.
Slide 16
PSPICE Simulation Results:
Shunt Diode’s Behavior
MM and HBM ESD threshold of the TMR head
increases when shunt diodes are applied.
Slide 17
● ESD Testing of TMR Heads
Shunt Diode’s Behavior
Shunt diodes can indeed increase the ESD threshold
of the TMR head.
Slide 18
What are the downsides of this method?
● The device has no protection from various ESD events throughout the entire fabrication and assembly.
● Only provides protection from Tester’s transients and
electrical overstress (EOS).
● The diodes can still be charged up when installed in
the Tester’s preamplifier.
Shunt Diode’s Behavior
Charging Mechanism of Diodes
Slide 19
● Diodes have diffusion capacitance (Cd) and zero p-n
junction capacitance (Cj).
● The charge stored in the neutral regions adjacent to
the junction.
● The amount of charge stored is proportional to the
forward current.
● Proportionality constant is called Transit Time (TT).
1nKT
qV
sf
f
eTTTTQ II
Slide 20
Charging Mechanism of Diodes
● Nonlinear charging mechanism leads to a nonlinear
capacitance.
● From Q = CV:- Increase in capacitance would increase the charge, Q.
Slide 21
● Effect of the Charge Storage Mechanism
- PSPICE Simulation Model
Charging Mechanism of Diodes
• This simulates an ESD event from the tester with
charged diode.
Slide 22
● Effect of the Charge Storage Mechanism
- PSPICE Simulation Results
Charging Mechanism of Diodes
Transient current in the TMR sensor increases with the
increase of charge at the diodes.
Slide 23
● Effect of the Charge Storage Mechanism
- Actual ESD Transient Measurement
Charging Mechanism of Diodes
• TEK CT-6 current probe with 200-ohm
simulated TMR resistance was used.
• Tap transient test was done at the HGA QST
and DET Tester’s TMR input pins.
Slide 24
● Effect of the Charge Storage Mechanism
- Actual ESD Transient Measurement Results
Charging Mechanism of Diodes
A Machine Model (MM) ESD event waveform was detected at
the Tester’s probe pins with shunt diodes!
On-Chip Diode Shunting
Slide 25
● Concept similar to the typical diode shunting.
● This method proposed that the diodes will be placed
into the TMR head itself.
Typical Diode Shunting On-chip Diode Shunting
Shunt diodes somehow does not affect the operating
signal, thus it installed into the TMR Head itself!
On-Chip Diode Shunting
Slide 26
● Protection Capability Comparison
No ShuntTypical Diode
Shunting
On-chip Diode
Shunting
Electrical Overstress (EOS)
X O O
ESD X X O
X – cannot protect O – can protect
Conclusions
● If installed in the tester’s preamplifier, diodes can still
be charged up, causing ESD transients.
Slide 27
● Diode shunting can increase the TMR head’s
threshold from EOS/ESD Events.
● Properly selected diodes can be installed into the
device as on-chip ESD protection.
● Diodes installed as on-chip ESD protection offers
protection all throughout the TMR head assembly
process.