C.I. Lee

Enhanced damage in linear bipolar integrated circuits at low dose rate

Enhanced damage at low dose rates was investigated for several different types of linear integrated circuits that were fabricated with conventional junction isolation. Although both npn and pnp transistors exhibit increased damage at low dose rate, the effect is far greater for substrate and lateral pnp transistors from these technologies. The saturation level of damage at high doses was also found to be far greater under low dose rate conditions than at high dose rates. A model for this behavior was developed that is consistent with earlier studies of MOS field oxides under low-field conditions, and accounts for the increased enhanced damage in pnp transistors.

Enhanced damage in bipolar devices at low dose rates: effects at very low dose rates

The effect of very low dose rate irradiation is investigated for several linear bipolar devices that are sensitive to enhanced low dose-rate damage, including one device with super-/spl beta/ input transistors. New results are included at 0.001 and 0.002 rad(Si)/s. Irradiations at elevated temperature at high dose rate are compared with room temperature irradiation at very low dose rate. Possible mechanisms for enhanced damage are discussed.

Total dose and proton damage in optocouplers

Radiation damage from gamma rays and protons is investigated for two types of optocouplers with different physical configurations. Far more damage occurs from protons because of displacement damage, which reduces the photoresponse of the phototransistor and causes severe degradation in LED light output for one of the two device types. The other device type was far more resistant to radiation, primarily because it used a shorter wavelength LED that was relatively unaffected by protons.

Total dose effects on Microelectromechanical Systems (MEMS): accelerometers

Microelectromechanical sensors, ADXL50 and XMMAS40G accelerometers which are fabricated with surface micromachining techniques are characterized for their total dose radiation response. Different failure mechanisms were observed when the sensor element or the whole device was irradiated.

Radiation response of a MEMS accelerometer: an electrostatic force

Particle irradiation on the mechanical sensor of the ADXL50 microelectromechanical accelerometer shifts the output voltage. An earlier conclusion, that a dielectric below the sensor becomes charged, is extended by quantifying the effect of this charge on device output. It is shown that an electrostatic force is consistent with the observation that the output voltage shift is independent of acceleration. Possible charging mechanisms are suggested. An appendix derives a convenient algorithm for calculating electrostatic forces, which may also be used for other MEMS devices.

Proton damage effects in linear integrated circuits

Proton tests of linear integrated circuits have identified devices where significantly more damage occurs at equivalent total dose levels with protons than with gamma rays. The difference is attributed to displacement damage, and it can be important for hardened devices as well as for unhardened technologies. Proton testing may be required for applications of circuits that use substrate and lateral pnp transistors in critical circuit functions where protons comprise a significant fraction of the space environment.

Degradation of precision reference devices in space environments

The degradation of precision reference devices is investigated to determine the relative importance of ionization and displacement damage. The results are compared with theoretical calculations of a basic bandgap reference circuit. Several of the device types were degraded severely at 20 krad(Si), with about the same degradation as that predicted for the basic bandgap reference circuit. One very high precision device with an internal heater performed far better than any of the other devices in the study.

Using commercial semiconductor technologies in space

New issues are discussed that must be considered when unhardened commercial technologies are used in space applications, as well as hardness assurance techniques. Large differences in dose-rate effects were observed for different circuit types from the same manufacturer, which may be due to differences in the thickness of isolation oxides used in processing. Data are presented for scaled MOS devices that show how total dose hardness and hard error rates are projected as devices are scaled to smaller feature size. Hard errors are expected to be a significant problem for devices with feature size below 0.6 /spl mu/m.

Total Ionizing Dose Effects In 12-bit Successive-approxmation Analog-to-digital Converters

Analog-to-digital (A/D) converters are critical components in many space and military systems, and there have been numerous advances in A/D converter technology that have increased the resolution and conversion time. The increased performance is due to two factors: (1) advances in circuit design and complexity, which have increased the number of components and the integration density; and (2) new process technologies, such as BiCMOS, which provide better performance, cost, and smaller size in mixed-signal circuits. High-speed A/D converters, with conversion rates above 1 MHz, present a challenge to circuit designers and test engineers. Their complex architectures and high-performance specifications result in numerous possible failure modes when they are subjected to ionizing radiation. The dominant failure mode may depend on the specific application because the fundamental effects on MOS and bipolar transistors are strongly affected by bias conditions.

Comparison of total dose responses on high resolution analog-to-digital converter technologies

Two different 12-bit analog-to-digital converter technologies, CMOS and BiCMOS, from Burr-Brown were compared for total dose responses. The BiCMOS converter appears to be a better candidate for space applications. CMOS devices showed larger degradation with both high dose rate (HDR) and low dose rate (LDR). An external voltage reference can be used for a radiation hardened process 12-bit converter from Analog Devices to maintain accuracy up to 1 Mrad(Si). DATELs 16-bit hybrid converter showed a low failure level with HDR.