Presentation on theme: "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 Li Hitachi."— Presentation transcript:
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 Li Hitachi 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
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 testers 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
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 HGAs Slide 8
Diodes Characteristic Slide 9 Diodes 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.
Diodes Characteristic Curves I-V Curves Slide 11 R-V Curves D1N5711 diode Turn-on voltage: 0.3 V Diode on Resistance, R d : 300 ohms TMR Heads nominal resistance: 500 ohms
Shunt Diodes 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 its operating voltage when diodes are installed.
Slide 13 Shunt Diodes Behavior TEK P6248 voltage differential probe connected across the TMRs 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 Diodes 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
Slide 15 During EOS/ESD Events - PSPICE Simulation Shunt Diodes Behavior This simulates a HBM and MM ESD events during testing or handling during fabrication and assembly.
Slide 16 PSPICE Simulation Results: Shunt Diodes Behavior MM and HBM ESD threshold of the TMR head increases when shunt diodes are applied.
Slide 17 ESD Testing of TMR Heads Shunt Diodes 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 Testers transients and electrical overstress (EOS). The diodes can still be charged up when installed in the Testers preamplifier. Shunt Diodes 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).
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 Testers 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 Testers 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 ShuntingOn-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 Shunt Typical Diode Shunting On-chip Diode Shunting Electrical Overstress (EOS) XOO ESD XXO X – cannot protectO – can protect
Conclusions If installed in the testers preamplifier, diodes can still be charged up, causing ESD transients. Slide 27 Diode shunting can increase the TMR heads 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.