Total dose effects on negative voltage regulator

Abstract

Functional failure at low dose level (4 Krad(Si)) on voltage regulators (LM137) from different manufacturers are analysed. Dose rate effects on parts hardness are evaluated, showing that lowering the dose rate degrade more the ICs in the range 55 rad(Si)/s-0,s rad(Si)/s A failure mechanism is proposed, mainly based on circuit analysis, voltage contrast measurements, local irradiation and local electrical measurements with probe station. A spice simulation was performed, providing quantitative informations on the degradation. In the light of such a failure analysis and dose rate Pagure (Saclay, France) panoramic Cobalt60 source of 20 000 Ci located few kilometres away from VBlizy plant. Remote testing were performed in VBlizy using LTS 2020 automatic tester from Analog Devices, Digital Signal Analyser DSA601 from Tekmnic and HP4172 from Helwett Packard. Delay between irradiation and remote testing is kept below one hour. Local irradiation are performed using scanning transmission electron microscope JEOL JSM840 with electron energy up to 40 Kev. Contrast voltage potential measurement were carried out using a IDS Shlumberger tester. Probing measurements were performed using Wentworth probe station MP900 and HP4145 from Helwett Packard. effects, practical implications on radiation assurance are discussed. FAILURE DESCRIPTION I. INTRODUCTIONBipolar linear ICs are usually known as quite hard parts regarding Total Dose effects, with typical dose hardness in the range 50 to 100 Krad(Si). Such a postulate comes mainly from the relative intrinsic high hardness of bipolar transistor and passive devices. The problem is that bipolar transistors and passive elements used in linear ICs are not similar to the well known elemental structures. Because of integration constraint and in order to minimise the number of mask steps during IC processing, PNP transistors are often lateral ones. Such a type of transistor is already known as Total Ionizing Dose (TID) sensitiveIl1. When using such a sensitive structure in critical function of linear IC, loss of functionality can be foreseen, as already predicted by Johnston 2. In this paper, we will focus on negative voltage regulator (LM137 type) from 4 different manufacturers. We will analyse the degradation mode, based on different test methods.LM137 is a three terminal adjustable output negative voltage regulator. Reference voltage of -1.250V can be delivered for input voltage (referred to output voltage) ranging from -4.2% to -41.25V. The 137 circuit, shown in figure 1, consists in start up circuit, intemal comparator, band gap reference, power output stage and prowtion circuitry. Figure 1 : Schematic diagramm of LM137. LM137 type parts from 4 manufacturers were irradiated with dose rate in the range 0,014 rad(Si)/s-55 rad(Si)/s in both static ON (see fig 14) and OFF mode (all pins grounded). For low dose rate (0,014 -0,25 rad(Si)/s) Cobalt 60 source Shepherd 484 located in MMS VBlizy plant was used. Higher dose rate (0.5 -56 rad(Si)/s) experiments were performed using The failure is a...

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