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      "title": "Explore in Atlas",
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    {
      "title": "imec — Entering the Nanosheet Transistor Era",
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      "title": "Gate-all-around nanosheet transistor",
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  "content": "Device physics · Atlas v1.3.0\n\n# Gate sidewall and inner spacers\n\nSeparates the gate from neighboring terminal structures and limits parasitic coupling.\n\n[Explore in Atlas](https://semiaifoundry.com/ai-atlas/#spacer)Nanometer-scale dielectric features; exaggerated in cutaway\n\nLearning objectiveExplain how spacers separate electrostatic and parasitic design goals.\n\n## The mechanism\n\nSpacers are small dielectric structures with large integration consequences. Around the gate, they provide separation from adjacent source/drain regions and contacts. In stacked nanosheet devices, inner spacers occupy regions between sheets near the gate ends, isolating gate material from the source/drain. Their shape influences unwanted gate-to-terminal capacitance and the space available for other device features. The atlas highlights these normally overlooked volumes in a cutaway rather than hiding them behind the gate shell. This is a structural explanation, not a manufacturing recipe: forming uniform spacers requires precise material selectivity and dimensional control. Without these separators, the impressive channel geometry would not translate into the intended electrical device.\n\n1.  Identify the small dielectric volumes between the gate and neighboring terminal structures.\n2.  For nanosheets, expose the inner spacers near the ends of the stacked sheets.\n3.  Relate their shape to electrical separation, unwanted capacitance, and available access space.\n\n## Science and assumptions\n\n### Parasitic capacitance and transition charge\n\n$$\nQ_{\\mathrm{par}}=C_{\\mathrm{par}}\\Delta V,\\qquad C_{\\mathrm{par}}\\propto\\frac{\\varepsilon_{\\mathrm{eff}}A_{\\mathrm{eff}}}{d_{\\mathrm{eff}}}\n$$\n\nTransition charge equals parasitic capacitance times voltage change. A qualitative capacitance model scales with effective permittivity and area, and inversely with separation.\n\nSymbols and units\n\nQ\\_par\n\nCharge moved into parasitic capacitance\n\nC\n\nC\\_par\n\nParasitic capacitance\n\nF\n\nΔV\n\nVoltage change\n\nV\n\nε\\_eff\n\nEffective absolute permittivity\n\nF/m\n\nA\\_eff\n\nEffective facing area\n\nm²\n\nd\\_eff\n\nEffective separation\n\nm\n\nEach voltage transition charges unintended gate-to-terminal coupling. Spacer geometry changes the effective field paths, connecting a tiny dielectric feature to switching-energy cost.\n\nAssumptions The geometric proportionality is a qualitative capacitor model; fringing fields dominate many real spacer structures and require numerical extraction.\n\n## Engineering example\n\nIncreasing effective spacer distance can reduce overlap capacitance but may increase access resistance or complicate source/drain formation.\n\n## Distinctions and tradeoffs\n\nSpacers are functional dielectric structures; deleting them for a cleaner rendering hides essential device anatomy.\n\nMore separation can lower capacitance. It also consumes space and can worsen access resistance.\n\nParasitic capacitance costs energy during switching. Spacer design helps preserve the efficiency promised by advanced transistors.\n\n## Specifications and interfaces\n\nMaterial class\n\nDielectric\n\nElectrically separates nearby structures.\n\nNanosheet feature\n\nInner spacers\n\nIsolation between gate and source/drain near sheet ends.\n\nKey effect\n\nParasitic capacitance\n\nGeometry changes unintended electrical coupling.\n\n### Interfaces\n\nAdjacent gate and terminals Input\n\nElectric fields and geometric proximity\n\nElectrical separation Output\n\nControlled spacing and reduced coupling\n\n## Check your understanding\n\n### What is one role of nanosheet inner spacers?\n\n1.  Transmit optical data through the chip\n2.  Replace all source/drain contacts\n3.  Separate gate material from source/drain and limit coupling\n\nAnswer and reasoning\n\nSeparate gate material from source/drain and limit coupling\n\nInner spacers contribute to the isolation and capacitance control required by the nanosheet geometry.\n\n## Evidence and scope\n\nThe parasitic relation is a proportional teaching model, not a process recipe.\n\nUse the switching investigation to connect physical charge, circuit load and arithmetic; the numerical library has no standalone model of this lesson’s full mechanism.\n\n## Sources\n\n-   [imec — Entering the Nanosheet Transistor Era](https://www.imec-int.com/en/articles/entering-nanosheet-transistor-era-0)\n\n[Published lesson data](https://semiaifoundry.com/ai-atlas/lesson-data/spacer-6a00ad1e827c9557.json) · [Atlas releases and licensing](https://semiaifoundry.com/ai-atlas/licenses.html)\n\n## Continue exploring\n\n### Foundations\n\n-   [Metal gate and high-k dielectric](https://semiaifoundry.com/learn/atlas/gate-stack/)\n-   [Source and drain regions](https://semiaifoundry.com/learn/atlas/source-drain/)\n\n### Related lessons\n\n-   [Gate-all-around nanosheet transistor](https://semiaifoundry.com/learn/atlas/gaa/)\n-   [Insulators and low-k films](https://semiaifoundry.com/learn/atlas/dielectric/)"
}