【Semiconductor】⚡ 08-09. What Is HCI? — Why High Electric Fields Destroy MOSFETs

topics: [“Semiconductor”, “HCI”, “Reliability”, “MOSFET”, “BSIM4”]

⚡ Introduction

In the previous article, we discussed
NBTI (Negative Bias Temperature Instability),
a reliability degradation mechanism dominated by time and temperature.

In this article, we focus on another major degradation mechanism:
👉 HCI (Hot Carrier Injection).

In other words, HCI represents:

“The price paid for pushing a device to operate faster and harder.”

🔥 What Is HCI?

HCI is a reliability degradation phenomenon that occurs in MOSFETs when:

Key characteristics include:

This clearly distinguishes HCI from NBTI.

🧠 What Is Happening Physically?

Near the drain region, MOSFETs experience:

As a result:

  1. Carriers are strongly accelerated
  2. They reach high-energy (hot carrier) states
  3. Some carriers are injected into the gate oxide
  4. Interface states and oxide traps are generated

👉 The MOSFET damages its own gate oxide.

This is the essence of HCI.

📉 Impact on Device Characteristics

HCI-induced damage manifests as:

Most importantly, these effects are observed as:

Changes in DC characteristics after prolonged high-$V_d$ operation

🆚 Difference Between NBTI and HCI

Aspect NBTI HCI
Primary device pMOS nMOS
Dominant factor Time, temperature Electric field, voltage
Damage location Interface states Interface + oxide
Main effect $V_t$ shift Mobility loss, $I_d$ reduction
Dependence Time-dependent Voltage / field-dependent

👉 They are fundamentally different degradation mechanisms
👉 Their mitigation strategies are also different

📐 How BSIM4 Treats HCI

In BSIM4, HCI is represented by:

However, an important limitation must be noted:

BSIM4 alone does not directly simulate time evolution

Therefore, SemiDevKit adopts a hybrid approach:

🧰 HCI Analysis with SemiDevKit

The following module is used:

This framework provides fully automated:

🔬 HCI Analysis Flow

t = 0
 ├─ VG–ID sweep
 │     ├→ Vtg0 (gmmax method)
 │     └→ Vtc0 (constant-current method)
 ├─ DC extraction
 │     └→ Idlin0 / Idsat0

t > 0
 ├─ Apply ΔVth(t) model
 ├─ Apply ΔId(t) model
 ├─ Reconstruct Vtg1 / Vtc1 / Idlin1 / Idsat1

→ Export CSV results
→ Generate degradation plots
→ Overlay VG–ID curves

🚀 Execution Example

cd bsim/bsim4_analyzer_reliability/run
python run_hci_nmos.py

📊 Example Results

■ NMOS HCI: Vg–Id Degradation (Linear Scale)

👉 Reduced $g_m$ and on-current
👉 A direct cause of critical-path delay increase

■ NMOS HCI: ΔVtg vs. Stress Time

👉 Early-stage degradation dominates
👉 Higher voltage conditions accelerate degradation

⚠️ Why HCI Matters

HCI is strongly linked to:

It clearly illustrates the trade-off:

“Chasing performance shortens device lifetime.”

🔗 TCAD / BSIM / SPICE: A Single Continuous Chain

HCI fits naturally into the same framework as previous topics:

👉 Physics → Model → Circuit → Degradation

This single conceptual chain is completed in the HCI chapter.

📚 Series Summary

Throughout this series, we consistently followed this path:

  1. TCAD (physical phenomena)
  2. BSIM4 (compact modeling)
  3. Paramus (model generation)
  4. SPICE (DC / AC / CV analysis)
  5. DIM (L/W scaling)
  6. Reliability (NBTI / HCI)

With SemiDevKit, it is possible to experience the entire flow without relying on commercial EDA tools.

📝 Summary

MOSFETs are no longer judged by:

“How fast can they run?”

but by:

“How long can they keep running fast?”

🔗 Related Links