strained silicon
Strained silicon is a technique that deliberately stretches or compresses the silicon crystal lattice in a transistor's channel region, altering how easily electrons or holes move through it and improving transistor switching speed without shrinking the transistor itself.
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**Strained silicon exists because a transistor's switching speed depends significantly on how easily electrons or holes can move through its channel, and that mobility can actually be improved by deliberately altering the silicon crystal's natural atomic spacing, not just by shrinking the transistor further.** Since introducing a controlled mechanical strain, either stretching or compressing the silicon lattice depending on the specific transistor type, changes how charge carriers interact with that lattice, often making it noticeably easier for them to move through it, strained silicon delivers a real transistor performance improvement that's independent of, and complementary to, continued transistor size scaling.
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```
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| Aspect | Unstrained silicon | Strained silicon |
|---|---|---|
| Lattice spacing | Natural, unaltered | Deliberately stretched or compressed |
| Carrier mobility | Baseline | Improved |
| Achieved via | N/A | Engineered material stress |
| Common use | Older, simpler transistor designs | Standard technique at modern nodes |
**Strained silicon uses different strain types, tensile stretching or compressive squeezing, depending on whether the transistor carries negative or positive charge carriers, since each carrier type responds differently to each strain direction.** Because electrons and holes respond differently to how the silicon lattice is deformed, transistor designs typically apply tensile strain for one transistor type and compressive strain for the other, tailoring the specific strain technique to whichever charge carrier that particular transistor relies on.
**Strain is commonly introduced through specific structural techniques, such as embedding a different material with a naturally mismatched lattice spacing directly into the transistor structure near the channel.** Rather than trying to strain the silicon lattice through some external force, chipmakers often introduce strain by growing or embedding a different crystalline material with a slightly different natural atomic spacing right next to the channel region, and that lattice mismatch mechanically strains the adjacent silicon as the two materials meet.
**Strained silicon's mobility benefit provided a genuinely useful performance boost as pure transistor size scaling began yielding diminishing returns, making it an important complementary technique in the industry's broader performance roadmap.** Because continuing to shrink transistors alone eventually faces diminishing performance returns and mounting difficulty, strained silicon offered chipmakers a complementary way to keep improving transistor performance that didn't depend purely on making transistors smaller, making it a significant technique in sustaining continued performance gains.
Read strained silicon through a stretched-lane lens: much like slightly widening a crowded lane can let people walk through it more easily without changing how many people are using it, stretching the silicon lattice makes it easier for charge carriers to move through, improving performance without needing to shrink the transistor itself.