ESD培训资料(Hitachi).pdf
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1、Hitachi Confidential1February 12,2009CDK 2004 Hitachi Global Storage TechnologiesHSPC Training SeriesHSPC 培训系列培训系列Part 3:The ContextClass 13:Understanding ESD 第第13课:理解课:理解ESDSam LuoChris KeenerTranslated by Yuan XiaoyuHitachi Confidential2February 12,2009CDK 2004 Hitachi Global Storage TechnologiesU
2、nderstanding ESD:Outline 概述概述ZAP!?Thermal Stability 热稳定性?Facts about thermal stability&ESD 热稳定性与ESD事例?Human Body Model HB模型?Symptoms in the head as a function of ESD magnitude ESD脉冲强度对磁头的效应?Effect of varying ESD pulse duration 变化ESD脉冲持续时间的效应?Pinned Layer Flipping 钉扎层翻转?Quiz 问题Hitachi Confidential3Fe
3、bruary 12,2009CDK 2004 Hitachi Global Storage TechnologiesThermal Stability 热稳定性热稳定性?Thermal instability is amplitude decay that occurs when heads are stressed at high temperatures 热不稳定性指磁头在高温热应力下幅值衰减的现象热不稳定性指磁头在高温热应力下幅值衰减的现象?The predominant mechanism for thermal instability is diffusion of atoms wi
4、thin the sensor 热不稳定性主要来自读头内部原子扩散效应热不稳定性主要来自读头内部原子扩散效应?Diffusion is temperature driven:热扩散热扩散?T=T Tambient I2R?where T is the maximum temperature at the stripe center 此处此处T指读头中心处的最高温度指读头中心处的最高温度?Note that Lifetime is extremely sensitive to bias voltage 注意读头寿命对偏压极为敏感注意读头寿命对偏压极为敏感?GMR 5.0 has better t
5、hermal stability than GMR 4.2 相对于相对于GMR4.2,GMR5.0具有更好的热稳定性具有更好的热稳定性d d It can run hotter 能工作在更高的温度能工作在更高的温度d d Bias Voltage can be increased 可提高偏压可提高偏压d d Performance is enhanced even with similar R/R 相同相同R/R条件下,综合性能增强条件下,综合性能增强?ESD is thermal decay on a short time scale/ESD是瞬时热衰减是瞬时热衰减?Human body m
6、odel 150 nsec 人体人体150纳秒纳秒?Machine model 10 nsec:equilibrium T not reached 机械机械10纳秒:未达到平衡温度纳秒:未达到平衡温度()273+TkEaeLifetimeHitachi Confidential4February 12,2009CDK 2004 Hitachi Global Storage TechnologiesThermal Stability:General Observations 热稳定性的一般现象热稳定性的一般现象?Thermal stress causes heads to change in 2
7、 ways 热应力对磁头的影响有两种方式:Amplitude decay(irreversible)幅值衰减(不可逆)Caused by diffusion of atoms in the sensor 来自读头内的原子扩散 Follows Arrhenius Law with activation energies consistent with atomic diffusion 依从Arrhenius 法则:激活能源于原子扩散 Bias voltage in HDD is designed to maintain a maximum sensor temperature 110 C 设计时
8、,硬盘中的偏压维持最大读头温度110 C We want heads to maintain high amplitude for 100,000 hours of continuous use 期望读头连续使用100,000 中保持高幅值Amplitude spreading(reversible)幅值分散(可逆)Most likely caused by settling of the free layer orientation into equilibrium 极可能来自于自由层磁化方向 This happens relatively quickly even at low stres
9、s temperatures(HDD operating temperatures and typical usage times,maybe on the order of 100-1000 hours)即便在低的热应力下也可能发生此现象(HDD 长时间运行会产生热量)Amplitude can increase or decrease,depending on the heads bias point and details of its stress and mechanical defect(e.g.,grain boundary)distribution幅值可能增大也可能减小,依赖于
10、磁头的偏压点和其应力机械缺陷(如:晶粒边界)的分布Hitachi Confidential5February 12,2009CDK 2004 Hitachi Global Storage TechnologiesESD:General Observations ESD的一般现象的一般现象?ESDTypical heads are damaged in 100 nsec by currents of 13 mA(20 VHBM)一般磁头在电流13 mA(20 VHBM)下100 nsec便被损坏HBM threshold varies inversely with resistance(as s
11、tripe height is changed)HBM门限值与电阻成反比(当SH 改变时)This means that the ESD threshold is approximately a constant Voltage for all heads of a given design(GMR type,MRW,gap)此意味着对于给定设计(GMR类型,读宽,间隙),ESD电压门限值对所有磁头是一个常数ESD threshold across sensor itself varies linearly with MRW 穿过读头本身的ESD门限值与读宽变化成线性关系 However,le
12、ad resistance is a significant component of total resistance 然而,引导层的电阻占总电阻的大部分 So ESD Voltage threshold varies roughly as MRW0.65(empirical function)因此,ESD电压门限值粗略随MRW0.65变化(经验公式)Hitachi Confidential6February 12,2009CDK 2004 Hitachi Global Storage TechnologiesHuman Body Model HB模型模型?Human Body Model
13、is a standardized ESD experiment HB模型是标准的ESD实验The head is placed in series with 1.5 k 磁头与一系列1.5 k电阻相连HBM Voltage is discharged from a 100 pF capacitor through the resistor and the head HB模型电压来自100pf电容器释电流过电阻和磁头HBM Voltage is actually proportional to the current through the head 实际HBM电压正比于流过磁头的电流Head
14、 resistance is much less than 1.5 kOhm 磁头电阻远小于1.5 kOhmConsider head resistance constant 50?Current=VHBM/1.55k 假设磁头电阻为常数50?电流=VHBM/1.55k 时间常数Time constant =1.55 k x 100 pF=155 nsec?This is a low frequency pulse that allows the head to nearly reach thermal equilibrium 此为低频脉冲允许磁头几乎接近热平衡Hitachi Confiden
15、tial7February 12,2009CDK 2004 Hitachi Global Storage TechnologiesWhat happens to the head as ESD becomes more severe 严重严重ESD对磁头的影响对磁头的影响?Typical amplitude and resistance profile as a function of ESD 典型幅值与电阻随ESD电压增强的变化图HBM Voltage0%20%40%60%80%100%120%N.Amp-50510152025Delta RScope of the workthis wor
16、kother worksSmall pulsesNo damageNo problem小脉冲没问题小脉冲没问题SevereDamageDead headAmp=0Large Resistance m严重m严重ESD磁头损坏幅值为磁头损坏幅值为0电阻增大电阻增大Mild ESDInstabilityAmp m中等m中等ESD不稳定性幅值增大不稳定性幅值增大PermanentESD damageAmp o oResist.m mSlightly永久永久ESD磁头受损幅值降低电阻增大磁头受损幅值降低电阻增大Sam Luo paperSEM FA:Invisible 扫描电镜失效分析:未见扫描电镜失效
17、分析:未见ESD|See spot at sensor 读头存在读头存在ESDHitachi Confidential8February 12,2009CDK 2004 Hitachi Global Storage TechnologiesWhat a Dead Head Looks Like 受损读头的外观受损读头的外观?Only dead heads(zero amp&high resistance)show visible evidence of physical damage 仅仅读头(0幅值和高电阻)表现出可见的物理缺陷Dead Head死头死头(RH open)Sensor mel
18、ted读头融化读头融化Almost dead head(RH open)Good head好头好头Hitachi Confidential9February 12,2009CDK 2004 Hitachi Global Storage TechnologiesDistribution of ESD pulses produces heads with different symptoms 不同征兆的不同征兆的ESD磁头的分布磁头的分布?Assume a hypothetical distribution of ESD pulses 假设ESD脉冲的近似分布?The long tail of h
19、igh-current pulses produces a range of symptoms 高电流脉冲部分?Thus we see some heads with:High amplitude(many of which are unstable)高幅值(许多为不稳定磁头)Negative amplitude(flipped,discussed a few pages later)负幅值(钉扎层翻转)Low amplitude 低的幅值Resistance(RH)very high(open),dead heads)极高的电阻(磁头损坏)Pulse amplitude脉冲幅值Number
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