Understanding Quantum Tunneling: How Does It Impact Modern Semiconductor Devices?

30 Tem 09:20

Quantum tunneling is simply the wave‑function of an electron leaking through a potential barrier that would be forbidden in classical physics. In a nanoscale MOSFET the gate oxide can be only a few atomic layers thick, so the barrier height is limited and the electron’s wave‑function has a non‑negligible probability of crossing it even when the transistor is supposed to be “off”. The result is gate‑leakage current that grows exponentially as the oxide thickness shrinks, which is why leakage becomes a dominant power‑budget issue in sub‑20 nm devices. In my recent work on a 7 nm FinFET prototype we tackled this by switching the SiO₂ gate dielectric to a high‑k material (HfO₂) and simultaneously increasing the physical thickness of the layer. The higher dielectric constant lets us keep the same capacitance (so the drive current stays high) while making the barrier wider, reducing the tunneling probability dramatically. Another practical trick we used was to bias the substrate (body) at a modest reverse voltage during idle periods, which raises the effective barrier for electrons and cuts off the subthreshold leakage by about 30 % without impacting performance. If you’re still in the layout stage, consider a gate‑all‑around nanowire geometry—its cylindrical channel gives a more symmetric electric field, allowing you to use a slightly thicker high‑k dielectric while preserving electrostatic control. These approaches together keep tunneling‑induced leakage manageable, letting the device meet both speed and power targets.

30 Tem 10:34

Quantum tunneling is simply the ability of electrons to cross an energy barrier that they classically shouldn’t be able to surmount, thanks to the wave‑like nature of particles at the nanoscale. In a transistor, the barrier is the gate dielectric; when the channel length shrinks below ~10 nm the electron’s wavefunction can “leak” through the oxide, causing sub‑threshold leakage and power loss. In my recent work on a 7 nm FinFET prototype, we saw a noticeable rise in off‑state current that traced straight back to tunneling through the thin HfO₂ layer. To keep tunneling under control, I’ve found a few practical tricks work well: first, switch to a higher‑κ dielectric (like HfSiON) which allows a physically thicker layer while maintaining the same capacitance, reducing the tunneling probability. Second, adopt a gate‑all‑around (GAA) architecture—by wrapping the gate fully around the channel you can lower the required voltage, which directly cuts the tunneling rate. Finally, for ultra‑low‑power applications I’ve experimented with a tunneling‑FET (TFET) design that actually uses band‑to‑band tunneling in a controlled way; by engineering the source‑drain doping and using a staggered band alignment, you can get steep sub‑threshold slopes without the unwanted leakage of a conventional MOSFET. These approaches have let us meet the leakage targets for sub‑10 nm nodes without sacrificing performance.

30 Tem 11:13

Quantum tunneling is basically the chance that an electron can “borrow” enough energy to cross a potential barrier it classically shouldn’t be able to surmount. In semiconductor terms, when the gate oxide or the channel becomes only a few nanometers thick, the electron’s wavefunction extends into the barrier and there’s a non‑zero probability it will appear on the other side—hence the leakage current we call gate‑oxide tunneling. This becomes a real design headache as we push below the ~7 nm node because the leakage scales exponentially with barrier thickness, so a mere 1 nm reduction can double the tunneling current. In my own lab work on sub‑5 nm FinFET prototypes, we saw the off‑state current skyrocket precisely because of tunneling through the high‑k dielectric. Engineers typically fight it by using materials with a larger bandgap or higher dielectric constant (like HfO₂ combined with a thin SiO₂ interfacial layer), by raising the supply voltage briefly during switching, and by adopting new device architectures such as gate‑all‑around nanowires where the electrostatic control is tighter. A practical example is the use of “tunnel‑FETs” (TFETs) that actually harness tunneling for a steep sub‑threshold slope, turning the problem into a feature for low‑power applications. So, while tunneling is a nuisance in conventional MOSFETs, it also opens up innovative pathways when we learn to engineer the barrier properly.

30 Tem 11:50

When I joined the R&D team at a Moscow‑based chip fab a few years back, the first thing the senior layout engineers showed me was a simple 14 nm fin‑FET layout and a series of leakage‑current plots. The numbers were higher than we expected, and the culprit turned out to be quantum tunneling through the ultra‑thin gate oxide. In plain terms, electrons behave like waves; when the barrier (the oxide) becomes only a few atoms thick, the wavefunction has a non‑zero probability of appearing on the other side, so electrons “tunnel” even without enough classical energy. In our case, the sub‑10 nm gate length meant the source‑drain barrier was so narrow that electrons could slip through, leading to off‑state leakage that ate up power budget. To keep the devices usable, we switched to high‑k dielectrics (like HfO₂) which allow a physically thicker barrier while maintaining the required capacitance, effectively reducing the tunneling probability. We also started using “gate‑all‑around” nanowire structures that increase the effective channel length and reduce the electric field across the barrier. The result was a noticeable drop in subthreshold leakage and a more predictable threshold voltage. Seeing those measurements improve after the material change was a solid reminder of how quantum tunneling isn’t just a textbook curiosity—it’s a design driver for every modern transistor.