Punchthrough

Punchthrough refers to a phenomenon in electronic circuits where a semiconductor device, typically a diode or transistor, experiences a sudden and irreversible breakdown of its electrical characteristics. This usually occurs when the applied voltage exceeds a certain threshold, causing excessive current to flow. The high current density can lead to localized heating, which in turn can permanently damage the semiconductor material, often by melting or creating a conductive filament.

In diodes, punchthrough is sometimes called reverse breakdown. When a reverse voltage is applied, a depletion region forms. If the reverse voltage is too high, the depletion region can extend across the entire device, allowing current to flow. In transistors, punchthrough can occur in bipolar junction transistors (BJTs) or field-effect transistors (FETs). For BJTs, it can happen when the collector-emitter voltage is high enough to cause the collector depletion region to reach the emitter. For FETs, it typically involves the drain voltage becoming so high that the drain depletion region extends all the way to the source.

The consequences of punchthrough are usually catastrophic for the device, rendering it inoperable. This can manifest as a short circuit or a significant change in resistance. Preventing punchthrough involves careful design considerations, including limiting the operating voltage to within the device's specified breakdown voltage and ensuring proper thermal management to dissipate heat generated during operation. Understanding and avoiding punchthrough is crucial for the reliability and longevity of electronic circuits.