{"id":"spacer","level":"transistor","name":"Gate sidewall and inner spacers","shortName":"Spacers","role":"Separates the gate from neighboring terminal structures and limits parasitic coupling.","description":"Spacers 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.","specs":[{"label":"Material class","value":"Dielectric","context":"Electrically separates nearby structures."},{"label":"Nanosheet feature","value":"Inner spacers","context":"Isolation between gate and source/drain near sheet ends."},{"label":"Key effect","value":"Parasitic capacitance","context":"Geometry changes unintended electrical coupling."}],"interfaces":[{"name":"Adjacent gate and terminals","direction":"in","signal":"Electric fields and geometric proximity"},{"name":"Electrical separation","direction":"out","signal":"Controlled spacing and reduced coupling"}],"tradeoff":"More separation can lower capacitance. It also consumes space and can worsen access resistance.","whyAI":"Parasitic capacitance costs energy during switching. Spacer design helps preserve the efficiency promised by advanced transistors.","related":["gate-stack","source-drain","gaa","dielectric"],"sources":[{"title":"imec — Entering the Nanosheet Transistor Era","url":"https://www.imec-int.com/en/articles/entering-nanosheet-transistor-era-0"}],"scale":"Nanometer-scale dielectric features; exaggerated in cutaway","kind":"spacer","mechanism":["Identify the small dielectric volumes between the gate and neighboring terminal structures.","For nanosheets, expose the inner spacers near the ends of the stacked sheets.","Relate their shape to electrical separation, unwanted capacitance, and available access space."],"misconception":"Spacers are functional dielectric structures; deleting them for a cleaner rendering hides essential device anatomy.","check":{"question":"What is one role of nanosheet inner spacers?","options":["Transmit optical data through the chip","Replace all source/drain contacts","Separate gate material from source/drain and limit coupling"],"answer":2,"explanation":"Inner spacers contribute to the isolation and capacitance control required by the nanosheet geometry."},"branch":"Device physics","subbranch":"Parasitic electrostatics","science":[{"title":"Parasitic capacitance and transition charge","equation":"Q_par = C_par ΔV; C_par ∝ ε_eff A_eff / d_eff","explanation":"Each voltage transition charges unintended gate-to-terminal coupling. Spacer geometry changes the effective field paths, connecting a tiny dielectric feature to switching-energy cost.","assumptions":"The geometric proportionality is a qualitative capacitor model; fringing fields dominate many real spacer structures and require numerical extraction."}],"history":[],"learningObjective":"Explain how spacers separate electrostatic and parasitic design goals.","engineeringExample":"Increasing effective spacer distance can reduce overlap capacitance but may increase access resistance or complicate source/drain formation.","evidenceNotes":"The parasitic relation is a proportional teaching model, not a process recipe.","visualFamily":"device-crosssection","prerequisites":["gate-stack","source-drain"],"labId":"library","scope":"Use the switching investigation to connect physical charge, circuit load and arithmetic; the numerical library has no standalone model of this lesson’s full mechanism.","investigationId":"switching","labScope":"Use the switching investigation to connect physical charge, circuit load and arithmetic; the numerical library has no standalone model of this lesson’s full mechanism."}