Aging Analysis Common Model Interface Gains Momentum

By Greg Curtis, Ahmed Ramadan, Ninad Pimparkar, and Jung-Suk Goo

In February 2019, Siemens EDA wrote an article¹ entitled “The Time Is Now for a Common Model Interface”. Since that time, we have continued to see increasing demand for aging analysis, not only in the traditional automotive space, but also in other areas of technology design, such as mobile communication and IoT applications to address long term reliability validation. This demand has placed requirements on foundries to provide aging models to satisfy their customers’ needs for accurate simulation of device aging over time, as this has become an integral step in the verification process.

In the past, aging effects were often mitigated with overdesign, at the cost of valuable chip real estate. However, designs today have to be optimized for each design parameter in order to absolutely minimize the chip real estate. This minimization of chip real estate cannot be fully realized without accurately estimating the long term impact of aging.

Two important mechanisms that contribute to device degradation are the Hot Carrier Injection (HCI) and the Positive/Negative Bias Temperature Instability (PBTI/NBTI). HCI, more prominent for the N-type MOSFET transistors, is caused by electrons near the drain region experiencing impact ionization under high lateral electric field, gaining high kinetic energy that enables them to surmount the Si-SiO2 barrier and get injected into the gate oxide, generating interface or oxide defects. NBTI, more prominent in P-type MOSFET transistors, is another issue in aging. When a P-type MOSFET transistor gate voltage is negatively biased for long periods of time under high temperature, the Si-H bonds break along the Si-SiO2 interface, causing the generation of interface traps. Both mechanisms are significant at smaller process nodes because the gate dielectric is scaled to only a few atoms in equivalent thickness. Over time, these interface traps cause threshold voltage to increase and channel carrier mobility to degrade, decreasing circuit performance, shortening circuit lifetime, and introducing potential failures in the field.

Despite initial efforts to develop a standardized aging model that covered these effects, the semiconductor industry ecosystem could not converge, therefore all foundries and IDMs had to rely on their own home-grown aging models that represent their process technology behavior. Because of this, the foundries have had to support several model interfaces to integrate their aging models into circuit simulators, as a common, industry-standard interface solution did not exist. Similarly, simulation suppliers were also required to support their own, unique interface. This non-standard approach added complexity and increased support costs for both the supplier and end-user alike.

Why the Open Model Interface (OMI) is the standard solution

In April 2018, the Si2 Compact Model Coalition (CMC)² released the first version of the Open Model Interface (OMI), based on the TMI interface. The OMI interface provides users the flexibility to customize the CMC standard models to fit their own applications, all without touching the native implementation of these CMC standard models. The OMI supports both model parameters’ update and reliability simulation.

The OMI standard interface enables foundries, IDMs, and EDA vendors to focus their resources on supporting a single, common standard interface. Fabless companies and internal IDM design groups can also take advantage of whichever simulator they determine best for their technology mix. The CMC OMI Standard v1.0.0 supports the following models: BSIM4, BSIM-CMG, BSIMSOI, and HiSIM2. More CMC standard models are planned to be included in the next version of the OMI.

OMI offers an aging platform that enables aging modeling, simulation, and analyses, supporting any degradation mechanism (Figure 1). This platform can support Hot Carrier Injection (HCI), Bias Temperature Instability (BTI) and Time Dependent Dielectric Breakdown (TDDB). For BTI, it also includes recovery effects. Both a one-step aging simulation and the more accurate gradual aging simulations can be performed using the OMI aging flow. Foundries can provide a unified OMI shared library to their customers, protecting the foundry’s modeling IP, as part of their technology design kit, without the need to alter the base model libraries they provide to their customers today. They only need to add the OMI-Aging portion (OMI shared library & Aging model parameters’ set) to their package. The power of OMI is that it is simulator agnostic. This means that the same unified OMI shared library can be used across different simulators that support OMI.

Figure 1. OMI aging flow.

Siemens EDA, a leader and active member in the CMC, realized the key advantages of the OMI interface. The OMI standard has been supported by Siemens EDA’s Analog FastSPICE (AFS) simulator since December 2018 and since then, Siemens EDA has been working with key partners to benefit from that work.

Joint activity between Siemens EDA and GLOBALFOUNDRIES

GLOBALFOUNDRIES has supported aging simulation capabilities for more than 10 years, closely working with leading EDA vendors including Siemens EDA. A growing number of customers have been requesting OMI aging simulation capabilities. From a foundry point of view, the simulator agnostic features that OMI provides would lessen the implementation and QA burden required for supporting multiple SPICE simulators. GLOBALFOUNDRIES and Siemens EDA have been collaborating on enabling GLOBALFOUNDRIES aging models in the CMC OMI interface since early 2019. Siemens EDA has been very instrumental in this work and the initial offering of the GLOBALFOUNDRIES OMI aging is planned to be concurrent with legacy aging tools, starting from the most advanced node PDKs. However, the strategy will gradually migrate to the OMI aging.

Summary

Long term reliability has always been a focus for the automotive industry but is now expanding to include other areas of technology design. As a result, accurate simulation of device aging over time has become an integral step in the verification process. Through a collaborative effort, Siemens EDA and GLOBALFOUNDRIES are working together to ensure mutual customers are able to run aging simulation using GLOBALFOUNDRIES process technologies on Siemens EDA’s AFS Platform through the CMC industry standard open model interface (OMI).

References
1] https://semiengineering.com/the-time-is-now-for-a-common-model-interface/
2] Silicon Integration Initiative (Si2) Compact Model Coalition (CMC) http://www.si2.org/cmc/

Greg Curtis is a senior product manager at Siemens EDA.

Ahmed Ramadan is a senior product engineering manager at Siemens EDA.

Ninad Pimparkar is a senior member of the technical staff at GLOBALFOUNDRIES.

Jung-Suk Goo is a principal member of the technical staff at GLOBALFOUNDRIES.