Snapback and Postsnapback Saturation of Pseudomorphic High-Electron Mobility Transistor Subject to Transient Overstress

On-Chip Electro-Static Discharge (ESD) Protection for Radio-Frequency Integrated Circuits

“…4.14 is that the I-V curves of single-and dual-gate clamps have almost the same slopes when the voltage is less Table 4. 3) than 8 V. Beyond this, the single gate clamp enters the saturation region caused by temperature induced mobility degradation [63], whereas the dual-gate clamp exhibits a steeper curve stemming from the turn-on of the second current path. The different current conduction mechanisms can be explained in more details below using physical reasoning and TCAD simulation results.…”

“…4.12a), resulting in an increase in the lattice temperature and consequently a decrease in the electron mobility. This in turn increases the resistance and hence the voltage drop in SG1 [63]. In the contrast, for DG1, the creation of the additional current path in the AlGaAs layer owing to the presence of second gate keeps the resistance and voltage drop in such a device relatively constant.…”

“…4.14a resulted from the use of a four-diode string. It is noticed that the resistances of both single-gate and dual-gate clamps change at around 5 V. This can be attributed to a positive feedback due to the electron-hole pair generation near the drain junction and the turn-on of embedded parasitic lateral BJT [63]. Figure 4.14b shows the TLP I-V characteristics of DG pHEMT's having four different diode strings.…”

“…4.14a, SG1 enters the current saturation region when the current is higher than about 0.5 mA/μm (i.e., equivalent to 0.5 A). The saturation results from the flow of discharging current being limiting to the 2DEG channel and mobility deg- radation due to thermal effect [63]. Below this current level, SG1 does not saturate and operates in a region where the clamping voltage drops considerable when the current decreases.…”

“…4.1). A conventional singlegate GaAs pHEMT is usually used as the shunting apparatus [62], but the current conducting capability of such a device, and hence the GaAs pHEMT-based ESD protection clamp, is still quite limited due to the self-heating and current saturation mechanisms [63].…”