DRAM 1968 Memory Needs Different Structure Than Logic

# Why Memory Needs an Entirely Different Structure Than Logic: The First Device This Project Has Built for Persistence, Not Speed

## 1. Why Every Earlier Series Built a Device That Forgets the Instant Its Input Changes

Every series this project has documented since 1954 built a device evaluated entirely by its behavior at a single moment — how fast it switches, how much current it draws, how far its breakdown voltage extends — and every one of those devices, by design, forgets its own output the instant its input changes, because a logic gate's entire purpose is to compute a function of what is happening right now, not to remember what happened before. This series builds a device with the opposite requirement: it must hold a bit of information even after the signal that set it has disappeared, continuing to report that same bit correctly until something deliberately changes it or reads it away. No earlier series in this project's history needed a device with that property, because no earlier series needed a device whose own past mattered to its present output.

$$Y(t) = f\big(X(t)\big) \quad \text{(logic)} \qquad \text{versus} \qquad Y(t) = f\big(X(t), Q(t^{-})\big) \quad \text{(memory)}$$

where $X(t)$ is the input applied at time $t$, $Y(t)$ the output at that same moment, and $Q(t^{-})$ the device's own stored state an instant before $t$ — every logic gate this project has built computes $Y(t)$ from $X(t)$ alone, with no dependence on anything the device itself was doing a moment earlier, while this series' own device must compute $Y(t)$ from both the present input and its own prior state, a dependence on time this project has never needed to build a device around before.

A Function of Now, Versus a Function of Now and Before every device this project has built, beside the one this series requires LOGIC — EVERY EARLIER SERIES X(t) Y(t) no dependence on the device's own past MEMORY — THIS SERIES X(t) Y(t) Q(t⁻) feeds back into the output the device's own past state is a real input Y(t) = f(X(t)) → Y(t) = f(X(t), Q(t⁻)) — persistence, not speed, is this series' own axis every earlier series optimized how fast a device responds; this series needs it to remember at all

## 2. Real Diagram: The Simplest Physical Shape This Requirement Can Take

The diagram below previews, in outline, the physical structure the rest of this series will build in detail — a storage element capable of holding a charge, and a switch controlling when that charge can be reached from the outside, the simplest arrangement this project will show satisfies the persistence requirement Section 1 just stated.

A Switch, and Something That Holds a Charge the structure the rest of this series builds in detail, shown here in outline only ACCESS SWITCH built in Step 3 STORAGE CAPACITOR built in Step 4 the switch controls access; the capacitor supplies the persistence — every later step in this series refines this outline

## 3. The First Series This Project Has Ever Opened Without a Switching-Speed Concern

Every earlier series this project has opened began with a conflict between two properties a switch had to balance — resistance against breakdown voltage, speed against static power, alignment tolerance against parasitic capacitance — and every one of those conflicts was a conflict about how a device behaves at a single moment under a given bias. This series opens with no such conflict at all, because the property it needs has nothing to do with any single moment's behavior. A device can switch arbitrarily fast, draw arbitrarily little current, and still fail this series' own requirement completely if it cannot hold its own state once the signal that set it is gone — and conversely, this series' own eventual structure will turn out to be built entirely from pieces this project has already characterized for other reasons, repurposed here not for their speed or their power, but for whether they can be made to remember.

Step 1 does not introduce a new transistor, a new material, or a new fabrication technique; it introduces a new requirement — persistence across time — that no earlier series in this project's history ever needed a device to satisfy, and names the two pieces, a switch and something that holds a charge, this series will spend its remaining steps building.

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