MOSFET 1962 Step 14 Pmos Only Reliable Polarity 1962

# Confront Why Only PMOS Was Reliable in 1962: a Fixed Oxide Charge This Series Has Not Yet Named

## 1. A Constraint Steps 2-10 Worked Around Without Naming

Every working MOS device described across this series' first ten steps is implicitly a PMOS device, and that was not a design choice -- it was the only polarity 1962's oxide process could reliably deliver. Thermally grown silicon dioxide, as grown by the processes available in 1962, carries a positive fixed charge built into the oxide itself near the silicon interface, left over from the growth chemistry. That built-in positive charge shifts an n-channel device's threshold voltage toward values that are difficult to turn off reliably, while it merely requires a larger (but controllable) negative gate voltage for a p-channel device -- which is why RCA's and everyone else's early commercial parts were PMOS, not a symmetric choice between the two.

One Fixed Charge, Two Very Different Outcomes why 1962's oxide pushed every commercial part toward PMOS OXIDE GROWTH, 1962 positive fixed charge built into the oxide itself not yet controllable NMOS ATTEMPT charge shifts threshold low hard to turn off reliably not commercially viable yet PMOS, AS BUILT charge merely raises Vt controllable negative swing this is what shipped This is a different mechanism from the mobile-ion drift this series' own Step 7 already covers. Step 7 is about contamination after fabrication; this is a property of the oxide growth itself.

## 2. A Constraint, Not a Permanent Limit

The fixed oxide charge is a property of the growth chemistry available in 1962, not an immovable law -- cleaner growth ambients and better process control would later reduce it enough to make reliable NMOS, and eventually complementary (both-polarity, "CMOS") devices practical, a thread this project's own 1963 CMOS-invention series and later experimental-logic series pick up for a different device generation. This step names the constraint only; the fix belongs to that other content, not here.

Fixed Oxide Charge Over Time a 1962 constraint, not a permanent one for the technology 90 1962 process 50 mid-1960s refinement 15 later controlled growth The downward trend is what makes later NMOS and CMOS devices practical. That story belongs to this project's cmos_invention_1963 and experimental_mos_bipolar_logic series, named here only.

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