With constant down-scaling and increasingly demanding requirements to the speed and functionality of ultra-high density integrated circuits, the need for scalability and advanced performance of ESD devices is also increasing. Additionally, highly scaled semiconductor devices, such as Fin Field Effect Transistor (FinFETs) device, are especially vulnerable to ESD stress.
An ESD event is a high current (up to 2 amps), short duration (typically 150 nanoseconds), high voltage (up to 2 kilovolts) event. Therefore, an ESD protection device must not turn on until the ESD voltage increases above the highest operating voltage of the devices it is supposed to protect, but must generally be able to turn on within 1 nanosecond (ns) before the ESD voltage reaches a level that would damage such devices. The ESD device must be able to clamp the ESD voltage at as low a level as possible in order to avoid damaging any semiconductor devices. Further, the ESD device must be able to shunt more than an amp of the ESD current to ground. ESD devices are generally implemented on all input and output (I/O) devices, between power lines (if possible) and between power lines and ground.
Prior art ESD devices utilize the heavily doped source/drain regions of FinFETs together with the underlying lightly doped well portion of the bulk substrate to form an NPN bipolar transistor in series with a ballasting resistor. Problematically, these types of ESD devices typically clamp the ESD voltage between 3.5-5 volts (V) and can only carry about 0.7 amps (A) before being damaged.
Another prior art ESD device utilizes the surrounding semiconductor structure of a FinFET to form a silicon-controlled rectifier (SCR) device in order to clamp the ESD voltage and shunt the ESD current. These SCR devices can carry much larger currents than the NPN transistor devices. However, the SCR devices do not typically turn on until the ESD voltage reaches 15 volts or higher, which will damage many semiconductor devices that need protection.
Accordingly, there is a need for an ESD device that turns on at a voltage level that is higher than the highest operating range of the devices it is supposed to protect and lower than a voltage level that will damage such devices. Additionally, there is a need that the ESD device should be able to clamp the ESD voltage at a very low voltage, for example at 3 volts or less. Further there is a need for an ESD device that can shunt the ESD current at levels above 1 A without being damaged.