Albert Wallash

Electrical breakdown and ESD phenomena for devices with nanometer-to-micron gaps

The current vs. voltage and electrical breakdown behavior for devices with micron and sub-micron gaps between conductors is studied. The limitations of the well-known but often-misinterpreted Paschen curve are discussed. The little-known modified Paschen curve, that includes field emission effects so important in understanding breakdown behavior for devices with sub-micron gaps, is described. Current vs. voltage measurements across metal-air-metal, metal-insulator-metal and metal-insulator-air-insulator-metal gaps with gaps ranging from 4 nm to 4 μm are reported. The breakdown voltage for an air gap of 0.9 μm was found to be 150 V, far below the Paschen curve minimum breakdown limit, and field emission behavior was confirmed via the Fowler-Nordheim plot. Metal-insulator-metal gaps with a diamond-like carbon thin-film with a thickness of 4 nm had a breakdown voltage of only 1V. SEM and AFM analysis show that the breakdown damage is crater-like and through the carbon layer. Other characterization of the damage caused by breakdown is presented. Tribocharging, electrostatic induction, and other ESD-related phenomena, are discussed for several devices with sub-micron gaps. It is concluded that devices with sub-micron gaps can face a serious challenge due to electrical breakdown during manufacturing, handling and operation. These devices include photolithographic reticles, magnetic recording heads, MEMS and field emission displays.

Degradation of GMR and TMR recording heads using very short duration ESD transients

Electrostatic discharge (ESD) testing results for giant magnetoresistive (GMR) and tunneling magnetoresistive (TMR) recording heads using a direct charged device model (D-CDM) tester are reported for the first time. The D-CDM is intended to replicate the ESD event produced by metal-to-metal contact discharge that occurs as a charged component discharges to another object at a different electrostatic potential. This discharge, through a very short path to ground, corresponds to an extremely fast (<1 ns wide), high-amplitude current transient. The D-CDM tester produces a transient by first charging the device itself and then grounding the device with a mercury relay. The ESD testing was done in situ with a quasi-static tester (QST) on GMR recording heads. Resistance, amplitude, asymmetry, and transfer curves were recorded after each ESD event. D-CDM physical failure voltages are much lower (4-5 V) than the ones obtained with the human body model (HBM) (25-30 V). Magnetic failure threshold can be even lower. We also report some D-CDM damage on TMR recording heads.

Electrostatic discharge and electrical breakdown study of the head-disk interface in a hard disk drive

A systematic and comprehensive procedure for understanding electrostatic discharge and electrical breakdown at the head-disk interface in a hard disk drive is described. First, the resistance, breakdown and field emission behavior for the individual and combined carbon overcoat films on the disk and slider was determined through current versus voltage testing. Second, different electrostatic mechanisms that can produce a voltage difference between the disk and slider or read transducer were studied. Results are explained in terms of the relative time constants for the voltage on the head and disk. It is concluded that a potential difference between the disk and recording head as little as 2 V can result in electrical breakdown damage at the head-disk interface.

New early failure phenomenon in electrostatic discharge damaged giant magnetoresistive recording heads

The magnetic behavior of partially electrostatic discharge (ESD) damaged giant magnetoresistive (GMR) heads during thermal and bias current stress is studied. Heads were ESD damaged to a level that would still pass quasistatic specifications and then monitored while at a higher temperature (100 °C or 150 °C) and bias current (5 to 6 mA) for up to 40 h. While controls showed no early changes, significant changes in amplitude, asymmetry, and Barkhausen jump were seen within the first hour of stressing in 10% of the partially ESD damaged heads. Heads that experienced pinned layer reversal or developed Barkhausen jumps were especially prone to large changes in magnetic response during stressing. It is concluded that some partially ESD damaged GMR heads can exhibit spontaneous and large degradation in amplitude and magnetic stability during high thermal and bias current stressing.