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Sentinel Silicon


Sentinel Silicon library includes precision measurement structures for:
TDDB - Time Dependent Dielectric Breakdown
HCI - Hot Carrier Damage
NBTI - Negative Bias Temperature Instability
Radiation Damage - RadCell Fox (Field Oxide) and RadCell VT (Threshold Voltage)

NBTI

  • Early-warning sentinel of an upcoming threshold voltage failure condition caused by NBTI degradation mechanisms
  • Size: 250 μm x 250 μm at 0.13 μm process
  • Instantiated in 130 nm CMOS;can be targeted toward any deep submicron CMOS technology
  • Power dissipation of approx.200 microwatts
  • Prognostic distance adjustable from nominal 80% point
  • Simple buffered logic high or low output indicates impending failure event
  • Pipeline architecture
  • 4-bit variable gain
 

General Description:
Negative Bias Temperature Instability (NBTI) is an effect that causes a gradual shift in transistor threshold voltage (VT). It manifests as an absolute drain current IDsat decrease, transconductance (gm) decrease, and absolute threshold voltage increase. NBTI is primarily observed in p-channel MOSFETs when the gate-to-source voltage is negative.
NBTI is caused by charged defect densities in the gate oxide interface region. The VT shift is dependent on voltage stress on the gate terminal, the temperature, and the duty cycle of the stressing voltage. Typical stress levels required to induce NBTI are temperatures in the 100 to 250 ºC range and electric field conditions across the oxide region higher than 6 MV/cm.The effects of NBTI are of increasing concern as device sizes move to 130 nm and smaller, and operating voltages decrease. As shown in Figure 1, the percent of remaining useful life can be determined with trigger points for the stress voltage, frequency, and duty cycle between the stress and measure cycles.

NBTI Block

TDDB

  • The Ridgetop TDDB Prognostic Built-in Self-Test (BIST) cell acts as an early-warning “sentinel” of an upcoming gate oxide failure condition due to Time-Dependent Dielectric Breakdown (TDDB)
  • Power consumption is approximately 600 microwatts
  • Size: 500 μm2 at the 0.13 micron process size
  • Prognostic “distance” breakdown can be scalable using design equation
  • Detects both hard and soft breakdowns

General Description:
Ridgetop’s TDDB Prognostic BIST Cell is a pad-limited CMOS leakage detection cell. Its unique and proprietary architecture behaves as an early-warning “sentinel” of upcoming gate oxide failure.
The amount of pre-warning is dependent on the prognostic distance, which depends on the area and the stress voltage.The TDDB cell is designed to be co-located with the host circuit and subjected to the same environmental stresses. These environmental stresses contribute to aging of the circuit and can include over- and under- voltage conditions, transient spikes, radiation exposure, humidity, and excessive temperature conditions.The TDDB prognostic cell is approximately 500 μm2 at the 0.13 micron process size. The cell is co-located on the same substrate as the host circuit, and shares the power and physical environment for optimum tracking of the aging effects. Estimated power consumption of the cell is approximately 500 microwatts.

 TDDB

HCI

  • Acts as an early-warning “sentinel” of upcoming degradation of MOS transistors caused by high-energy electron injection into the gate oxide. Damage occurs in the form of localized charge trapping, which causes a decrease in drain current ID and an increase in threshold voltage (VT).
  • Inspects drain avalanche hot carrier (DAHC) injection and channel hot electron (CHE) injection
  • Approx. 600 mW power
  • 500 μm2 footprint at 0.13 micron process
  • Measures in present of delta VT shift of 2, 4, 6, 8, and 10%
 

General Description:
Promoting miniaturization without scaling the supply voltage implies increasing the electric field intensity of the internal elements of a device. This is especially true in the case of MOSFETs, where the electric field intensity near the drain area increases and a hot carrier degradation effect occurs.

Carriers (electrons) that flow into the high-electric-field area are accelerated by the strong field, and gain substantial energy. Some of the carriers become a hot carrier, which means they have enough energy to overcome the electric potential barrier existing between the Si substrate and gate oxide film. These degradations cause the deterioration of all semiconductor device characteristics and ultimately lead to failure.

HCI 

VT

  • Predicts threshold voltage (Vt) failure due to radiation exposure
  • Available for various CMOS processes
  • Power dissipation is approximately 600 μW
  • Prognostic distance can be adjusted from nominal 80% point
  • Simple buffered logic high or low output indicate an impending failure event
  • Optional IEEE-1149.1 JTAG Bus interface
 

General Description:

Total dose radiation exposure results in charged defect densities in the gate and isolation oxide regions of a MOS transistor. The charged defects degrade device performance by introducing changes in threshold voltage (Vt) and leakage current. The magnitude of the parametric shift is dependent on operating conditions and environment. The Ridgetop RadCell Vt prognostic cell (Figure 1) accurately senses radiation-induced shift in CMOS transistor threshold voltage and outputs the cumulative degradation result

The output is derived from a family of sensor cells, designed and calibrated to trigger at specific values of threshold voltage shift. The RadCell Vt prognostic cells reside on-chip with the host application, and are implemented using the device types and geometries available in the target process. This allows the prognostic cell to identically replicate the transistors used in the host application, and makes the output useful in determining the effects of environmental stress on the application’s performance and service life.

VT

 

FOX

  • Predicts leakage failure conditons caused by radiation exposure
  • 800 μm2at the 0.25 micron process size
  • Available for 0.35, 0.25, and 0.18 micron CMOS processes
  • Power dissipation approx. 50 μW
  • Prognostic distance adjustable from nominal 80% point
  • Simple buffered logic high or low output indicates an impending failure event
  • Optional IEEE-1149.1 JTAG Bus interface

General Description:
Total dose radiation exposure results in charged defect densities in the isolation and gate oxide regions of a MOS transistor. The charged defects degrade device performance by introducing changes in threshold leakage current and voltage. The magnitude of the parametric shift is dependent on operating conditions and environment. The Ridgetop RadCell Fox prognostic cell accurately senses the radiation-induced leakage current in CMOS transistors and outputs the cumulative degradation result. The output is Product Description derived from a family of sensor cells, designed and calibrated to trigger at specific values of leakage current. The RadCell Fox prognostic cells reside on-chip with the host application, and are implemented using the device types and geometries available in the target process. This allows the prognostic cell to identically replicate the transistors used in the host application, and makes the output useful in determining the effects of environmental stress on the application’s performance and service life.
RadCell Fox prognostic cells can be used as a diagnostic tool, relating device-level parametric shifts to circuit-level performance, or to allow comparison of laboratory test results with field performance. The output of the prognostic cell can also be used as the input for an adaptive-bias control circuit. Multiple cells can be combined with calibrated prognostic distances to accurately track cumulative degradation, consistent with the requirements for condition-based maintenance. VT