Confront Why the First Working Mos Devices Were P Channel Not N Channel

# Confront Early PMOS Polarity: Why the First Working Devices Were P-Channel, Not N-Channel

## 1. Why Every Early Experimental MOS Device Used a P-Channel, Against the Intuitive Choice

The residual trapped charge Step 4 characterized was, in virtually every early oxide, net positive — and a net positive fixed charge at the interface pulls the threshold voltage of an N-channel device toward large positive values (making it hard to turn on) while pulling a P-channel device's threshold toward easily reachable negative values (making it comparatively easy to turn on), so the first practical experimental MOS devices and the first MOS integrated demonstrations were built P-channel, not because P-channel was intrinsically preferred but because the available oxide's own charge polarity made N-channel devices impractical to turn on reliably with the gate voltages available. The threshold comparison that forced this choice:

## 2. Real Diagram: The Mobility Cost This Forced Choice Imposed

The forced choice carried a real performance penalty the industry would not be free to ignore indefinitely: hole mobility in silicon is intrinsically lower than electron mobility, so a P-channel device, all else equal, switches more slowly or needs a larger channel for the same current than an N-channel device would — a cost paid specifically because the available oxide left no other practical option in the early 1960s.

## 3. The Mobility Cost This Forced Choice Imposed

This mobility penalty is exactly the kind of cost Step 7's gate-capacitance comparison against bipolar switching energy has to carry honestly: early PMOS is not simply faster or lower-power than bipolar RTL in every respect, it trades one disadvantage (mobility) against another (standing current), and the next several steps follow both sides of that trade without pretending one side is free.