2010 eos/esd symposium a study on the application of on- chip eos/esd full-protection device for tmr...

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


● Results





● 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


● Results





● 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


● Results





● 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.


• 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


- 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

● During EOS/ESD Events

- PSPICE Simulation


• This simulates a HBM and MM ESD events during

testing or handling during fabrication and assembly.

PSPICE Simulation Results:


MM and HBM ESD threshold of the TMR head

increases when shunt diodes are applied.

● ESD Testing of TMR Heads


Shunt diodes can indeed increase the ESD threshold

of the TMR head.

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.


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


● Nonlinear charging mechanism leads to a nonlinear

capacitance.

● From Q = CV:- Increase in capacitance would increase the charge, Q.

● Effect of the Charge Storage Mechanism

- PSPICE Simulation Model


• This simulates an ESD event from the tester with

charged diode.


- PSPICE Simulation Results


Transient current in the TMR sensor increases with the

increase of charge at the diodes.


- Actual ESD Transient Measurement


• 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.


- Actual ESD Transient Measurement Results


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.

2010 eos/esd symposium a study on the application of on- chip eos/esd full-protection device for tmr...

Documents

diodes characteristic

shunt diodes behavior

hgas slide

mv slide

diodes capability

diodes characteristic

charged diode

probe diode