Impact of laser pulse duration to induce Single Event Upset (SEU)
Pulsed lasers have proven to be a very economical and fast alternative to testing Single Event Effect as compared to radiation sources. When it comes to inducing the Single Event Upset by pulsed lasers in semiconductor devices, there are four parameters that are of importance. There are:
The absorption coefficient of Silicon depends on the optical wavelength as shown in the figure 1. One can see that the 8000 nm beam penetrates deeper into the bulk of the material.
· The total number of electron hole-pairs generated in the device depends on the laser pulse energy. This is shown in figure 2.
Figure 2: The number of upsets depends on the laser pulse energy
· The spatial density of electron-hole generation rate also depends on the spot size of the focused beam and this has to be as small as possible to increase the fidelity of the technique. This is shown in Figure 3
Figure 3: The SEE threshold energy increases as a function of laser spot size [Ref1]
· Finally the last factor is the effect of pulse duration on inducing the single event effect which is the topic of this technote. The pulse duration specifies the generation rate [Ref 2, Ref3]. Figure 4 shows the dependence of threshold energy on the pulse duration.
Figure 4: Dependence of threshold pulse energy on pulse duration [Ref 2]
Considering the fact that for a pulsed laser, procurement, maintenance and operation costs are inversely proportional to its pulse duration, the choice of laser with a certain pulse duration is quite important. The interaction of the charged particle in the real space environment takes place over a ps time scale. Several researchers have used pulsed lasers for SEE testing with a pulse duration ranging from less than 1 ps to nanoseconds [Ref 2]. If the pulse duration is too long, the observed effects may not accurately simulate the real life scenarios.
Figure 4 shows three distinct regions where the pulse duration affects the behavior of the threshold pulse energy as a function of pulsed duration. In region 1, which covers range of less than 1 pico-second to about 30 pico-seconds, the threshold pulse energy is independent of the pulse duration and its value is at a minimum. In region IIa, which is between 30 pico-seconds and 8 ns, there is a gradual increase in threshold pulse energy as a function of pulse duration. Past 8 nsec, in region IIb, the threshold pulse energy increases linearly with pulse duration.
Allied Scientific Pro offers Single Photon Absorption (SPA) testing stations with 1064 nm lasers that have a pulse duration of 30 ps. The system comes with illuminators, SWIR cameras, translation stage and microscope objective. ASP also offers access to its lab services on a rental basis and customers could test their systems without purchasing the system to gain confidence in the ability of the pulses laser SEE station in providing the results they are looking for. The following link has more information.
1- The laser-only single-event effects test methods for space electronics based on ultrashort-pulsed laser ‘local irradiation’, O. Mavritskii et.al, SPIE digital library.
2- Influence of laser pulse duration in Single Event Upset testing, A.Douine et.al, IEEE Transactions n nuclear science, Vol 53, No.4, August 2006.
3- Pulsed-Laser testing for Single-Event Effects Investigations, Stephen Buchner et.al, IEEE Transactions n nuclear science, Vol 60, No.3, August 2013.