ESD protection device optimises transistor structure

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Analysis of 3D simulations has allowed Toshiba to identify a mechanism for optimising transistor structure to boost ESD robustness.

Toshiba now optimises the structure of transistor and improves electrostatic discharge (ESD) characteristics. The development of an ESD protection device for analogue power semiconductor application is fabricated with advanced 0.13μm process technology.

ESD protection is more robust, up four times, and the standard deviation is only 1/12 that of the conventional structure. Analysis of 3D simulations has also allowed Toshiba to identify a mechanism for optimising transistor structure to boost ESD robustness. The company announced these advances at “ISPSD2016”, the international semiconductor symposium held in Czech last June 14, 2016.

__Figure 1:__ *Schematic cross-section of studied structure. (Image source: Toshiba)*

Injections of ESD surges, whether from the human body or equipment, have the potential to destroy semiconductor devices, as ESD current flows cause local temperature increases inside silicon. ESD protection devices are required to protect internal circuit. This is especially true for analog power semiconductor devices required to apply 10V to 100V, which need a high rated voltage. In this case, ESD protection devices must ensure high current flow, which results in enlarged chip size. Shrinking the size of the ESD protection device is an issue in realising more compact chips.

__Figure 2:__ *3D-Simulation results for studied structure. (Image source: Toshiba)*

Using 3D simulation analysis of an ESD event, Toshiba found out that ESD induced destruction is caused by lattice temperature increase due to the current flowing at the highest electric field point. Modifying the transistor structure, which extending the drain low resistive region to the source direction and suppressing the lateral silicon resistance, shifts the current flow from the bottom of the drain to source direction and detaches it from the highest electrical field point. This optimised design was found to increase ESD robustness by up to four times and to decrease the standard deviation down to 1/12. In addition, the device size required to ensure HBM ±2000V was cut by 68%.

Toshiba offers advanced analog process platforms, with 0.13μm process technology, that can be embedded with the transistors such as CMOS, DMOS, bipolar transistor and the passive devices such as resistor and capacitor. User can select a process suited to each application from three process platforms: “BiCD-0.13” is mainly for automotive (DMOS line up is up to 100V); “CD-0.13BL” is mainly for motor control drivers (DMOS line up is up to 60V); and “CD-0.13” process is mainly for power management IC (DMOS line up is up to 40V).

Toshiba plans to release products using the CD-0.13 process applied in this technology in 2017 and proactively continue to implement to other process platforms to improve electrostatic discharge characteristics.