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现已发现两条输入保护电路之间出现新的闩锁失效模式。这种双向闩锁不同于传统闩锁模式,它可在辐射或电脉冲瞬变期间、在电源插销与地线插销之间产生低电阻。在双向闩锁情况下,如果电源经受峰值电压,两个输入锁之间就会形成两条低电阻通路,还会出现接通状态。在CMOS VLSI电路中,两端交流开关闩锁通路并不总是存在于每条输入保护电路中,它只有在p和n沟道MOS FET构成栅控二极管的输入ESD保护电路中才会出现。在这种电路结构中,这两个输入插销之间有一个典型双向p—n—p—n二极管。它具有对称正反方向SCR特性。在温湿偏压试验(THB)期间,通常在两条输入保护电路之间观测到突发性电过应力(EOS)失效。这种失效与正常THB加速应力的失效机理无关,但它类似于两个输入ESD保护插销之间的SCR闩锁烧毁。这个二端交流开关闩锁结构能产生导致器件失效的局部SCR闩锁。这种双向闩锁可用光电发射显微镜在输入保护栅控二极管上定位。
It has been found that there is a new latch failure mode between the two input protection circuits. This bidirectional latch differs from the traditional latching mode in that it produces a low resistance between the power pin and ground pin during radiation or electrical pulse transients. In the case of bi-directional latching, if the power supply is subjected to a peak voltage, two low-resistance paths are formed between the two input latches and the on-state is also present. In CMOS VLSI circuits, the two-terminal AC switch latch path is not always present in each input protection circuit, and only occurs in the input ESD protection circuitry that forms the gated diode with p- and n-channel MOS FETs. In this circuit structure, there is a typical bi-directional p-n-p-n diode between the two input pins. It has symmetrical positive and negative SCR characteristics. During warm-up bias test (THB), sudden electrical over stress (EOS) failure is usually observed between the two input protection circuits. This failure is not related to the failure mechanism of normal THB acceleration stress, but it is similar to the SCR latch burnout between two input ESD protection pins. This two-terminal AC switch latch structure can create a local SCR latch that can cause device failure. This bidirectional latch can be positioned on the input protection gated diode using a photoemission microscope.