【Semiconductor】 ⚙️ 08-04. Learning BSIM4 Model Generation with Paramus — Graduating from the Black-Box .model

topics: [“Semiconductor”, “BSIM4”, “SPICE”, “Model Generation”, “MOSFET”]

🧭 Introduction — Why .model Files Become Black Boxes

BSIM4 is a very powerful MOSFET compact model,
but in practice and education it is often treated as:

• “Model cards are given”
• “The internals are not to be touched”

As a result:

• Parameter changes cannot be logically explained
• Simulation results must simply be taken on faith

This is exactly the assumption that Paramus is designed to break.

In this article, we take the perspective of:

Generating a BSIM4 model yourself from physical parameters

with the goal of understanding the meaning behind a .model file.

🤔 Why Learn Model Generation?

The .model used in SPICE analysis
is not just a configuration file.

It contains a condensed summary of device physics, such as:

• Oxide thickness $t_{ox}$
• Substrate doping $N_A$
• Carrier mobility $\mu$
• Threshold voltage $V_{th}$

Once you understand model generation, you can:

Explain in your own words
why device characteristics change when a parameter is modified

⚙️ The Role of Paramus — Standing Between Physics and Circuits

Within SemiDevKit, the role of Paramus can be summarized as:

TCAD (Device Physics)
   ↓
Paramus (Physics → Model Translation)
   ↓
BSIM4 (SPICE-Usable Form)

👉 Paramus acts as a “translator.”

• Lighter than TCAD
• Closer to physics than BSIM4

It occupies this intermediate layer.

📥 Inputs and 📤 Outputs Matter

📥 Inputs (Physical Parameters)

• Oxide thickness $t_{ox}$
• Substrate doping $N_A$
• Carrier mobility $\mu$
• Estimated threshold voltage

📤 Outputs (BSIM4 Model)

• BSIM4 .model file
• Directly usable in SPICE

The key point is to generate the model while consciously tracking:

Physical quantities → BSIM4 parameters

🧠 Basic Philosophy of Model Generation

Paramus operates with the following simple workflow:

1. Accept physical parameters
2. Determine initial values for BSIM4 parameters
3. Embed them into a template

The emphasis here is on:

Meaningful initial values rather than aggressive optimization

👉 Not “does it fit?”
👉 but “why is this value reasonable?”

🧩 What It Means to Graduate from the Black Box

By using Paramus, you can track at the model level:

• What happens when $t_{ox}$ is changed
• How $V_{th}$ shifts with increased doping
• How mobility affects $I_d$

This intuition is essential for connecting:

• TCAD
• SPICE

and understanding how they relate.

🧪 Execution Environment in SemiDevKit

Paramus is included in the BSIM section of SemiDevKit.

🔗 Paramus Page
https://samizo-aitl.github.io/SemiDevKit/bsim/Paramus/

The generated .model files can be directly used for:

• DC analysis
• AC / CV analysis
• Reliability analysis (NBTI / HCI)

▶ What Comes Next — Using the Generated Model

Once the model is generated, the next phase is using it.

• Sweep gate voltage $V_g$
• Sweep drain voltage $V_d$
• Read the resulting $V$–$I$ characteristics

👉 A model is not finished when it is created.
👉 It gains meaning only when it is used.

📝 Summary

• Paramus is an educational tool for BSIM4 model generation
• It reveals the mapping between physical and model parameters
• Once you can question a .model, your understanding of SPICE deepens dramatically

▶ Next Article

👉 05: Reading MOSFET DC Characteristics with BSIM4
— Understanding model behavior through $V$–$I$ analysis

⚙️ From here, the series proceeds through
“Model Generation → DC Analysis → AC/CV → Reliability.”