2005 MAPLD, Paper 240 JJ Wang 1 Total Ionizing Dose Effect on Programmable Input Configurations J. J. Wang, R. Chan, G. Kuganesan, N. Charest, B. Cronquist

1 2005 MAPLD, Paper 240JJ Wang

Total Ionizing Dose Effect on Programmable Input Configurations

J. J. Wang, R. Chan, G. Kuganesan, N. Charest, B. Cronquist

Actel Corporation


Outline

Total Ionizing Dose Testing

Input Threshold TID Testing Data

Annealing Effect

Failure Analysis and Mechanism

Lesson Learned and TID Hardening


Total Ionizing Dose Testing

TM1019 Military Standard for TID testing (Fig 1)

Pass

Fail3 Post-Irradiation Functional Test

4 Post-Annealing Electrical Tests

1 Pre-Irradiation Electrical Tests

2 Radiate to Specific Dose

Redo Test Using Less Total Dose

Fig 1 TID testing flow


DUT and Irradiation

0.25µm CMOS technologyCommercial off-shore foundry

VCCI/VCCA = 5V/2.5VTTL I/O configurationDefense Microelectronic Activity (DMEA)Co-60 SourceDose Rate = 1 krad(Si)/min (±5%)Room temperature irradiationStatic biased irradiation

Fig 2 Picture showing Gamma-ray irradiator


Parameter Measurement

Parameters Logic Design

1 Functionality All key architectural functions

2 ICC (ICCA/ICCI) DUT power supply

3 Input Threshold (VIL/VIH) Input buffers

4 Output Drive (VOL/VOH) Output buffers

5 Propagation Delay String of buffers, Clock to Q

6 Transition Characteristic D flip-flop output

VIL defined as the start of low to high transitionVIH defined as the start of high to low transitionTTL trip point (average of VIL and VIH) ~ 1.5V, CMOS ~ 2.5V


Rad-induced Input Threshold Shift

Five (A, B, C, D, E in chronological order) lots from foundry X tested

2 lots (B, C) show VIL/VIH switching from TTL to CMOS

The number of events increases with total accumulated dose and can be removed by annealing

DUT Total DosePre-Irradiation Post-Irradiation

VIL (V) VIH (V) VIL (V) VIH (V)

B1 100 krad 1.25 1.48 1.26 1.53

B2 100 krad 1.24 1.48 2.29 2.52

B3 100 krad 1.25 1.47 1.25 1.47

B4 100 krad 1.25 1.49 1.23 1.51

B5 100 krad 1.25 1.47 2.32 2.55

DUT Total DosePre-Irradiation Post-Irradiation

VIL (V) VIH (V) VIL (V) VIH (V)

C1 60 krad 1.24 1.51 1.38 1.45

C2 60 krad 1.25 1.52 1.22 1.53

C3 60 krad 1.25 1.51 1.24 1.48

C4 100 krad 1.25 1.52 1.23 1.49

C5 100 krad 1.24 1.51 2.41 2.67

C6 100 krad 1.23 1.50 1.24 1.56

C7 100 krad 1.25 1.51 1.26 1.48

C8 100 krad 1.26 1.52 1.41 1.57

Table 1 Lot B Pre- and Post-Irradiation VT (Net 0)

Table 2 Lot C Pre- and Post-Irradiation VT (Net 0)


Post-Irradiation Input Threshold Switching from TTL to CMOS

Lot C is chosen for investigation

More design nets are tested for post-irradiation input threshold

Part to part and pin to pin dependence observed

DUT Total DoseNet 1 Net 2 Net 3 Net 4

VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V)

C1 60krad 1.43 1.46 1.38 1.44 1.39 1.46 NA NA

C2 60krad 1.39 1.5 1.41 1.47 1.41 1.49 1.21 1.56

C3 60krad 1.39 1.49 1.31 1.54 1.38 1.46 1.38 1.48

C4 100krad 2.59 2.63 1.42 1.48 2.57 2.64 1.4 1.55

C5 100krad 1.47 1.51 1.44 1.47 1.45 1.49 1.43 1.51

C6 100krad 1.39 1.53 1.35 1.49 1.38 1.5 1.4 1.53

C7 100krad 1.41 1.48 1.38 1.48 1.35 1.49 1.36 1.55

C8 100krad 1.42 1.52 1.43 1.49 1.42 1.49 1.41 1.49

Table 3 Lot C Post-Irradiation VT


Post-Irradiation Input Threshold Switching from TTL to CMOS

DUT Total DoseNet 5 Net 6 Net 7 Net 8

VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V)

C1 60krad 1.39 1.45 1.38 1.46 1.38 1.45 1.39 1.45

C2 60krad 1.4 1.52 1.39 1.55 NA NA 1.38 1.44

C3 60krad 1.37 1.47 1.37 1.47 1.32 1.46 1.36 1.45

C4 100krad 1.37 1.49 1.43 1.49 1.41 1.49 2.61 2.66

C5 100krad 1.47 1.51 1.45 1.51 1.42 1.48 1.42 1.48

C6 100krad 1.39 1.49 NA NA 1.4 1.62 1.51 1.63

C7 100krad 1.38 1.45 1.43 1.51 1.31 1.56 1.4 1.48

C8 100krad 1.44 1.47 1.44 1.48 1.42 1.47 1.43 1.47

Table 3 Lot C Post-Irradiation VT

DUT Total DoseNet 9 Net 10 Net 11

VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V)

C1 60krad 1.38 1.45 1.38 1.46 1.4 1.45

C2 60krad 1.38 1.45 1.22 1.58 1.41 1.49

C3 60krad 1.34 1.46 1.38 1.48 1.37 1.44

C4 100krad 1.41 1.47 1.38 1.54 1.36 1.46

C5 100krad 1.44 1.51 1.48 1.54 1.45 1.48

C6 100krad 1.37 1.49 1.37 1.57 1.37 1.48

C7 100krad 1.36 1.43 1.13 1.64 1.39 1.49

C8 100krad 1.42 1.49 1.43 1.5 1.42 1.48


Annealing Effect Experiment

DUTTotal Dose

Net 0 Net 1 Net 2 Net 3 Net 4 Net 5

VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V)

C9 100krad 1.36 1.49 1.37 1.49 1.37 1.48 1.33 1.46 1.40 1.49 1.39 1.48

C10 100krad 1.36 1.47 1.42 1.52 1.40 1.48 1.38 1.49 1.43 1.51 1.41 1.50

C11 100krad 1.36 1.49 1.40 1.51 1.39 1.49 1.38 1.50 1.40 1.50 1.41 1.50

C12 100krad 1.36 1.61 1.39 1.50 1.38 1.48 1.35 1.48 1.43 1.52 1.33 1.51

C13 100krad 1.34 1.53 1.37 1.52 1.36 1.54 1.35 1.50 1.34 1.54 1.25 1.59

DUTTotal Dose

Net 6 Net 7 Net 8 Net 9 Net 10 Net 11

VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V) VIL (V) VIH (V)

C9 100krad 1.41 1.51 1.38 1.46 1.37 1.46 1.35 1.46 1.44 1.53 1.34 1.45

C10 100krad 1.41 1.51 1.38 1.47 1.39 1.49 1.37 1.49 1.42 1.52 1.38 1.46

C11 100krad 1.41 1.52 1.39 1.48 1.39 1.48 1.38 1.50 1.41 1.51 1.37 1.46

C12 100krad 1.41 1.52 1.38 1.48 1.20 1.59 1.35 1.53 1.43 1.53 1.38 1.47

C13 100krad 1.35 1.55 1.43 1.52 1.42 1.52 1.36 1.49 1.41 1.51 1.43 1.53

Five DUT from lot C are irradiated to 100 krad with a lower dose rate (1 krad/hr)

No switching from TTL to CMOS observed


Focus Ion Beam Experiment

The internal node that is suspected being pulled down by radiation-induced leakage is FIB’ed for microprobing

However, the heat generated during the FIB process annealed the device and hence recovered the TTL input threshold from CMOS


Fabrication Process Dependence

Foundry X show TTL to CMOS switching in 2 out of 5 lots, more recent lots show no switching

Foundry Y doesn’t show TTL to CMOS switching in 3 lots

Variable material characteristics of the commercial foundry FOX (field oxide) determine the TID tolerance of this phenomenon


Configurable Input

As shown in Figure below, a popular way to vary the input threshold is to change the strength of the pull-down by changing the turn-on number of NMOSFET pull-downs

TTL (1.5V trip point) has more turn-on NMOSFET pull-downs than CMOS (2.5V trip point)

PAD

To core logic

Configuration Control

Fig 3 showing the simplified schematic of configurable input


Failure Mechanism

For testing the programmable switch, node X is holding high by a single weak pull-up for TTL configurationRadiation induced leakage in the NMOS pull-down device pulls node X down (after certain total dose) and switches the input configuration from TTL (trip point ~1.5V) to CMOS (trip point ~2.5V)

PAD

To core logic

Vref

Weak pull up

Radiation-induced leakage

Node X

Test Control Programmable Switch


Physical Mechanism

The charge generation, transport and trapping in a biased oxide layer. The primary effect in sub-micron device is the hole trapping near the Si/SiO2 interface.


Physical Mechanism


Physical Mechanism

Total dose induced edge and field leakage


Lesson Learned and TID HardeningAccelerated testing overestimates the effects caused by radiation-induced field leakages Commercial foundries have variable FOX characteristicsWeak pull-up is a weak spot for total dose effectCommercial design often is not perfectly radiation optimized due to time to market pressureTwo design options

1. Redesign the logic so there is no weak pull-up 2. Re-layout the leaky NMOSFET to “edgeless” (shown below)

Drain

Gate

Source

Documents

2005 MAPLD, Paper 240 JJ Wang 1 Total Ionizing Dose Effect on Programmable Input Configurations J. J. Wang, R. Chan, G. Kuganesan, N. Charest, B. Cronquist