Transient-Induced Latchup in CMOS Integrated Circuits under EFT Tests
6.2. Evaluation on Board-Level Noise Filter Networks
During system-level ESD tests, the bi-polar transient voltages (underdamped sinusoidal waveforms) disturbed on the VDD/VSS lines of CMOS ICs inside the EUT often cause malfunction or hardware damage of microelectronic products. It has been reported that the different types of board-level noise filter network can impact the dominant parameters of bi-polar transient voltage, such as transient peak voltage, frequency and damping factor, by suppress the ESD-induced voltage efficiently. Therefore, four types of board-level noise filters have been investigated in this section and the experimental measurement results are shown below. The measurement setup combined noise filter network with TLU test measurement instruments is shown in Fig. 6.1.
Fig. 6.1 Measurement setup for TLU test combined with noise filter network.
Different types of noise filter networks are investigated to find their effectiveness for improving the detection range of proposed transient detection circuit I under TLU tests, including: (1) capacitor filter, (2) type-I RC filter, (3) type-II RC filter, and (4) π-section filters based on the combinations with TVS and ferrite bead.
6.2.1. Board-Level Noise Filter Networks
It has been shown that noise filter networks can enhance immunity of CMOS ICs to system-level ESD test by decoupling, bypassing, or absorbing ESD-induced noise voltage (energy). It has also been reported that the noise filter networks have strong impact to the parameters of the underdamped sinusoidal voltage such as transient peak voltage, damping frequency, and damping factor. Four types of noise filter networks: capacitor filter, type-I RC filter, type-II RC filter, and π-section filter are depicted in Figs. 6.2(a), 6.2(b), 6.2(c), and 6.2(d), respectively. Figs. 6.3, 6.4, 6.5, and 6.6 shows their improvements on both positive and negative detection range enhancement of the proposed on-chip RC-based transient detection circuit I.
(a) (b)
(c) (d)
Fig. 6.2 Four types of noise filter network investigated for their improvements on the detection range of the proposed on-chip RC-based transient detection circuit I. (a) Capacitor filter, (b) Type-I RC filter, (c) Type-II RC filter, and (d) π-section filter.
6.2.2. Experimental Results of System-Level ESD Tests
The ceramic disc capacitor with advantages such as high rated working voltage (1 kV), good thermal stability, and low loss over a wide range of frequency is employed as the decoupling capacitor in the noise filter of Fig. 6.2(a). Decoupling capacitances ranging from 1 nF to 0.1 μF are used to investigate their improvements on the detection range of proposed on-chip RC-based transient detection circuit I. With the aid of the capacitor filter to reduce the electrical transient voltage on VDD, the positive detection range can be significantly enhanced from +9 V (without decoupling capacitor) to over +28 V (with a decoupling capacitance of 0.1 μF), as shown in Fig. 6.3 Similarly, the negative detection level can be also greatly enhanced from -2 V (without decoupling capacitor) to -37 V (with a decoupling capacitance of 0.1μF). Thus, by choosing a decoupling capacitor with proper capacitance value, a simple 1st-order decoupling capacitor placed between VDD and VSS (ground) of CMOS ICs can be used to appropriately improve the detection range of proposed on-chip RC-based transient detection circuit I under the TLU tests.
Fig. 6.3 Relations between the decoupling capacitance and the detection range of the proposed on-chip RC-based transient detection circuit I with capacitor filter.
The resistor, which is commonly used for degrading transient disturbance energy, sometimes substitutes for inductor as a 2nd-order type-I RC filter component, as shown in Fig.
6.2(b). Due to a higher insertion loss (2nd-order filter), such type-I RC filter has better detection range enhancements than capacitor filter (1st-order filter) in Fig. 6.2(a). For
example, with 5-Ω resistor on the type-I RC filter, the positive detection range can be significantly enhanced from +9 V (without decoupling capacitor) up to +25 V (with decoupling capacitance of 0.1 μF) , as shown in Fig. 6.4. Similarly, the negative detection range can be also greatly enhanced from -2 V (without decoupling capacitor) to -32 V (with decoupling capacitance of 0.1 μF). Thus, in order to achieve higher detection range, the type-I RC filter can be used to avoid an excessively or unreasonably large decoupling capacitance in a simple 1st-order capacitor filter.
Fig. 6.4 Relations between the decoupling capacitance and the detection range of the proposed on-chip RC-based transient detection circuit I with Type-I RC filter.
The resistor, which is commonly used for degrading transient disturbance energy, sometimes substitutes for inductor as a 2nd-order type-II RC filter component, as shown in Fig. 6.2(c). Due to a higher insertion loss (2nd-order filter), such type-II RC filter has better detection range enhancements than capacitor filter (1st-order filter) in Fig. 6.2(a). For example, the positive detection range can be significantly enhanced from +5 V (with resistor of 5 Ω) up to +13 V (with resistor of 150 Ω), as shown in Fig. 6.5. Similarly, the negative detection range can be also greatly enhanced from -2 V (with resistor of 5 Ω) to -4 V (with resistor of 150 Ω).
A 3rd-order π-section filter is used to further enhance the detection range of the proposed on-chip RC-based transient detection circuit I, as shown in Fig. 6.2(d). This π-section filter consists of a resistor and two decoupling capacitors with equal decoupling capacitance. With
the highest insertion loss among the noise filter networks in Figs. 6.2(a), 6.2(b), 6.2(c), and 6.2(d), the detection range of the proposed on-chip RC-based transient detection circuit I can be most improved. For example, the positive detection level can be significantly enhanced to over +400 V (with a decoupling capacitance of 0.1 μF), as shown in Fig. 6.6. Similarly, the negative detection range can also be significantly enhanced to over -63V (with decoupling capacitance of 0.1 μF). From the comprehensive measured results in Fig. 6.6, the decoupling capacitance can be optimized according to the desired detection level and the type of board-level noise filter chosen.
Fig. 6.5 Relations between the decoupling capacitance and the detection range of the proposed on-chip RC-based transient detection circuit I with Type-II RC filter.
Fig. 6.6 Relations between the decoupling capacitance and the detection range of the proposed on-chip RC-based transient detection circuit I with π-section filter.