Bardeen Brattain Point Contact Transistor Process Flow Hub
# Bardeen and Brattain's Point-Contact Transistor: The Complete 25-Step Process, From Germanium to Verified Amplification
Bardeen and Brattain's December 1947 point-contact transistor is documented here as a 25-step sequence: 22 mandatory steps that take rectifier-grade N-type germanium through material selection, point-contact construction, circuit wiring, and biased operation, followed by 3 separate refinements, published in 1948, that improve on the original construction without being required additions to it. Every step in this sequence has its own full article; this hub exists to show how the 25 fit together, and to make clear where the mandatory sequence ends and the optional refinements begin.
Material and surfaces, Steps 1 through 9, establish every property the device will depend on before a single point contact exists. Step 1 selects N-type germanium specifically because rectifier-grade purity does not, by itself, guarantee the minority-carrier lifetime a point-contact device actually needs. Step 2 cuts the body with enough machining allowance to remove the damage that cutting itself creates. Steps 3 and 4 prepare the contact face early, since nothing touches it again for many steps. Step 5 prepares the base face on a tighter schedule, immediately before metallization, because that face cannot tolerate the same delay. Step 6 deposits the broad, low-resistance base electrode. Step 7 mounts the body and attaches its lead, building for a spring mechanism that does not exist yet. Step 8 catches contamination that Step 6's metallization may have let stray onto the contact face. Step 9 conditions that face's own surface state, and Step 10's wash protects the result without undoing it.
Point contacts, Steps 10 through 16, build and finish the two objects that actually make the device active. Step 11 places a solder drop on a wire's point, a step whose subject is the wire, not the germanium. Step 12 attaches that formed point to a spring arm, closing a loop Step 7's mount opened by anticipating a force that had no source yet. Step 13 seats the first point under real tension, the first moment the germanium and point tracks actually touch. Step 14 places the second point near the first, producing the only actual spacing value this entire sequence works from. Step 15 forms both points with a current pulse, the one step that deliberately damages what every other step protected. Step 16 attaches the cartridge leads and seals the housing, the last point at which anything built so far can still be inspected or corrected.
Circuit and operation, Steps 17 through 22, add nothing physical to the sealed device and specify everything about how it is actually driven. Step 17 commits the base as the one terminal never assigned a carrier-selective role, making it the only terminal that can serve as a shared reference. Step 18 forward-biases the emitter, finally producing the injected current Step 1 chose N-type germanium to support. Step 19 reverse-biases the collector with the opposite sign at the same reference, and treats reverse breakdown voltage as the critical constraint Step 1 once dismissed as irrelevant. Step 20 connects a load that turns a current change into a measurable voltage. Step 21 applies the first time-varying signal in the sequence, bounded both by the bias point's linear region and by how fast injected carriers can actually cross the point spacing. Step 22 measures that output against the input and verifies both voltage amplification and real power gain, closing the question Step 1 opened on its first line.
The 1948 refinements, Steps 23 through 25, document improvements to the same construction without reopening the mandatory sequence. Step 23 names the two-independent-wire construction Steps 11 through 14 already used, contrasting it with the split-gold-foil wedge of the original December 1947 prototype. Step 24 finally reports the point spacing this entire series referenced in the abstract since Step 1: 1 to 10 mils, roughly 25 to 250 micrometers. Step 25 documents a second, optional forming method — sustained reverse bias through a current-limiting resistor — applied selectively to whichever contact Step 22's measurement shows actually needs it, rather than to both contacts automatically the way Step 15's current-pulse forming was.
| Step | Title | What it establishes | Row |
|---|---|---|---|
| 1 | Select N-Type Germanium | Rectifier-grade purity alone does not guarantee transistor action; minority-carrier lifetime is the property that does | 113329 |
| 2 | Cut a Small Block or Disc | The first operation that creates the damage every later step has to budget for removing | 113330 |
| 3 | Grind the Contact Face Flat | The point-contact face, ground early because its spacing standard has no urgency behind it | 113331 |
| 4 | Chemically Etch the Germanium | Removes the contact face's grinding damage through a self-smoothing mechanism grinding cannot substitute for | 113332 |
| 5 | Grind and Etch the Second Contact Area | The base face, finished immediately before metallization because it cannot tolerate the delay the contact face can | 113344 |
| 6 | Apply Copper or Gold | The broad base electrode, built by the opposite area strategy from the point contacts still to come | 113333 |
| 7 | Attach the Base Lead and Mount the Germanium | A mount and lead built in advance for a spring mechanism and a resistance budget that do not exist yet | 113334 |
| 8 | Re-Etch the Upper Face | The first genuinely conditional step, running only if Step 6's metallization strayed onto the contact face | 113335 |
| 9 | Condition the Active Surface | Sets the contact face's own electronic state deliberately, distinct from the bulk property Step 1 verified | 113336 |
| 10 | Wash Away the Treatment Residue and Dry the Surface | Removes Step 9's residue without undoing the surface condition Step 9 just established | 113337 |
| 11 | Place a Small Drop of Molten Solder on the Point | Switches the sequence's subject from the germanium body to the wire that becomes a point contact | 113338 |
| 12 | Attach the Formed Point to a Spring Arm | Builds the spring mechanism Step 7's mount had to anticipate before it existed | 113339 |
| 13 | Apply Spring Tension and Seat the Point Assembly | First contact between the germanium track and the point-and-spring track, under real load | 113340 |
| 14 | Place the Collector Point Near the Emitter Point | Produces the first actual point-spacing value; every earlier reference to spacing was a placeholder for this number | 113341 |
| 15 | Form the Point Contacts With an Electrical Current Pulse | Deliberately melts and recrystallizes a region at each point — the one step built to damage, not protect | 113342 |
| 16 | Attach the Cartridge Leads and Seal the Housing | The last step able to inspect or correct anything built since Step 1, before the interior is sealed for good | 113343 |
| 17 | Use the Base as the Common Reference Terminal | Commits the base as the one terminal with no carrier-selective role, making it the shared circuit reference | 113345 |
| 18 | Apply a Small Positive Emitter Voltage Relative to the Base | Forward-biases the emitter, producing the first actual injected current in the sequence | 113346 |
| 19 | Apply a Negative Collector Voltage Relative to the Base | Reverse-biases the collector; reverse breakdown voltage becomes the critical limit Step 1 once set aside | 113347 |
| 20 | Connect a Load in the Collector Circuit | Converts a collector current change into a voltage change — the first externally observable signal | 113348 |
| 21 | Apply a Small Signal Between Emitter and Base | Modulates injection for the first time; bounded by the linear region and by the point spacing's crossing time | 113349 |
| 22 | Measure the Response Across the Collector Load | Verifies voltage amplification and real power gain, answering the question Step 1 opened | 113350 |
| 23 | 1948 Refinement — Two Sharpened Spring Wires Instead of Split Foil | Names the independent two-wire construction Steps 11 through 14 already used | 113351 |
| 24 | 1948 Refinement — Set Their Separation and Pressure Carefully | Reports the actual spacing range, 1 to 10 mils, that earlier steps referenced only in the abstract | 113352 |
| 25 | 1948 Refinement — Optionally Electrically Form One or Both Contacts Using Reverse Bias | A second, selective, optional forming method distinct from Step 15's mandatory current pulse | 113353 |
This hub does not add a new argument to the sequence; it is the only article whose job is to show that twenty-five separate arguments add up to one continuous one. Every step above was written, deployed, and verified on its own, against its own specification, and each one depends on at least one earlier step's result without restating it. Reading any single step in isolation shows a real decision correctly made. Reading them in this order, from a material choice that could not guarantee transistor action to a measurement that finally confirms it, shows why each decision had to be made in the order it was.