Point Contact Transistor Form Points Current Pulse
# Form the Point Contacts With an Electrical Current Pulse: The One Step That Deliberately Damages What Every Other Step Protected
Every step since Step 2 has worked the same way: remove exactly the damage that a prior operation introduced, and protect whatever was carefully built from any damage going forward. Step 15 breaks that pattern on purpose. A pulse of current, passed through each point contact, locally melts a small region of germanium and solder together and lets it recrystallize — and that deliberate, controlled damage is not a side effect to be minimized. It is the entire point of this step. Until this pulse is applied, the assembly built across the previous thirteen steps is, at best, two ordinary rectifying point contacts sitting close together on a piece of germanium. Forming is the operation that has any chance of turning that into something that actually shows transistor action, the exact phrase Step 1 opened this entire series by warning was never guaranteed.
Forming works only because of a decision made eleven steps earlier. Step 11 chose the point contact's solder composition specifically for what a later forming pulse would turn it into when alloyed with germanium, a choice this series described at the time as electrical rather than merely mechanical, even though nothing could confirm that electrical consequence until now. This pulse is where Step 11's choice is finally exercised: the current melts the solder and a small volume of the germanium beneath it together, and as that molten region cools and recrystallizes, the alloy's composition — set back in Step 11 — determines what kind of region forms at the contact and whether it actually helps carriers cross the interface. A point contact formed with the wrong solder composition can receive exactly the right current pulse and still fail to show useful gain, because the pulse only activates a choice that was already either right or wrong.
The current is bounded on both sides, but this time the margin is narrower than anything earlier in the sequence, because the upper bound threatens the one measurement Step 14 just finished establishing. Too little current and the pulse does not melt enough material to form a useful region at all — the contact remains an ordinary rectifying point, and the device shows no transistor action regardless of how carefully every earlier step was executed. Too much current risks two different failures at once: it can destroy the fine point structure itself, and because the emitter and collector now sit only a few thousandths of an inch apart, an alloy region that grows larger than intended can physically approach or even bridge the gap Step 14 placed with such care, shorting the two points the entire sequence has worked to keep separate and independent.
This is also the first step whose specification is a measured outcome rather than a fixed target. Step 3 specified a roughness number. Step 12 specified a stiffness number. Step 14 specified a separation distance. Every one of those specifications could, in principle, be verified by measuring the object against a predetermined value. Forming cannot be specified that way with the same confidence, because the quantity that actually matters — whether the formed contact shows real gain — depends on the combined, imperfectly predictable outcome of the solder composition, the germanium's local condition, and the pulse itself, interacting in a melt-and-recrystallize event that is not fully controllable from the outside. This step is typically monitored and adjusted against the device's own live electrical response as the pulse is applied, rather than executed once against a number decided in advance — the first step in this sequence where the device being built is also the instrument used to tell whether the step itself succeeded.
| Step | Process operation | Input | Output | Specification | Constraint |
|---|---|---|---|---|---|
| 15.1 | Confirm emitter and collector seating and separation remain as verified in Step 14, immediately before forming | Jointly verified two-point assembly from Step 14 | Confirmed-ready assembly | Position and tension unchanged from Step 14's final verification | Forming an assembly that has already drifted out of Step 14's spacing compounds an unresolved problem with an irreversible one |
| 15.2 | Determine the forming current range from the solder composition chosen in Step 11 and the germanium's known response | Solder composition from Step 11, germanium carrier type from Step 1 | Target forming current range | Lower bound set by the minimum melt needed to form a useful region; upper bound set by point-destruction and spacing-bridging risk | A current range set without reference to Step 11's specific solder composition risks a pulse calibrated for the wrong alloy behavior |
| 15.3 | Apply the current pulse to the first point contact while monitoring the device's live electrical response | Confirmed-ready assembly from 14.1, target current range from 14.2 | First point, formed, with measured response | Measured response showing the onset of useful gain, not merely current flow | A pulse applied without live monitoring can only be judged correct after the fact, when adjustment is no longer possible |
| 15.4 | Apply the current pulse to the second point contact, accounting for any change the first pulse made to local conditions | First-point-formed assembly from 14.3 | Both points formed | Second pulse calibrated with awareness that the first pulse may have altered the shared local region between the two points | Treating the second point's forming as independent of the first ignores that the two points no longer sit in an undisturbed, symmetric local environment |
| 15.5 | Re-verify emitter-collector separation and absence of a bridging alloy region after both points are formed | Both-points-formed assembly from 14.4 | Spacing-verified formed assembly | Measured separation still within Step 14's tolerance; no detectable alloy bridging between the two formed regions | A forming pulse that stayed within the current range can still have grown an alloy region large enough to compromise the spacing Step 14 established |
| 15.6 | Record forming current, monitored response, and post-forming verification against both points' provenance | Verified formed assembly from 14.5 | Documented formed point-contact assembly | Current levels, measured response, and spacing verification recorded against each point's record from Step 11.6/11.6 | Without this record, a later device failure cannot be distinguished between an under-formed contact, an over-formed contact, or a spacing fault introduced by forming itself |
Step 15 does not finish building the point contacts; it is the first step that finds out whether building them correctly was enough. Every specification in the previous thirteen steps — the germanium's carrier type, its diffusion length, its roughness, its conditioned surface, the solder's composition, the spring's stiffness, the two points' separation — was a necessary condition this step now tests jointly, for the first time, under a process that cannot be fully predicted from the outside and cannot be undone once applied. A device that fails to show transistor action after this step does not necessarily mean this step was done wrong; it may mean any one of the thirteen steps before it was. That is what makes this step different from every one before it: it is not where a new property is added to the device, but where the series finally learns whether everything it already built was actually right.