Tech Tour of Metal Gate I/O Transistors

Kevin Gibb, Product Line Manager, TechInsights
EETimes (1/11/2016 00:01 AM EST)

No one talks about the workhorse of the metal gate CMOS transistors -- the input/output (I/O) transistor. TechInsights thinks they are worth a look.

Much has been written about metal gate CMOS transistors for low-voltage applications such as processors and system on chip (SoC) devices. But these devices are connected to the outside world and require input/output (I/O) transistors that support higher bias voltages. Little is said about input/output (I/O) transistors. We at TechInsights think that they are worth a look.

We begin with a polysilicon gate I/O transistor, in this case from a 28nm node MediaTek part fabbed by TSMC (Figure 1). The I/O transistor has a fairly long gate length (160nm) that is typical of I/O transistors. This long gate length reduces the magnitude of the lateral electric field in the channel region beneath the gate. We care about this lateral field as it gives rise to hot carrier injection of electrons (NMOS) or holes (PMOS) from the channel into the gate dielectric that can degrade the transistor’s electrical performance.

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