Single Event Upset, also known as Soft Error Upset
(A temporary incorrect state of the circuit)
DUT = Device Under Test

To determine the radiation susceptibility of your IC design to Alpha Particles
and Secondary Cosmic Rays (Energetic Neutrons), Alpha Sciences can provide
a means of inducing high energy ion beams by means of a cyclotron facility.
This will provide latchup screening, single event, and total dose and dose rate
characterization. At the bottom of this section you will find a typical Statement
of Work, indicating the objective of the testing.

But first, a brief section on SEU...

When an ionized particle interacts with a semiconductor, electron-hole pairs
are generated along the path of the incident particle. These generated
electron-hole pairs can be transported through the semiconductor by drift
and diffusion processes, which ultimately can generate transient device currents.
Under certain biasing conditions the transient currents can alter the previously
stored state of the circuit, causing an error in the data stored in the circuit. This
phenomenon is generally referred to as Single Event Upset (SEU).

In memory devices the SEU has two attributes:

1) the data read from an address differs from the data originally
written to that address, and
2) the absence of physical damage or degradation to the memory,
which continues to function normally thereafter.

In 1978, the first evidence of SEU from energetic particles was given in a famous
paper by May and Woods of Intel. The paper resulted from an investigation of
upsets in the 2107 series 16K DRAM. It was discovered that the upsets were
caused by trace radioactivity in the memory packaging materials.

Naturally occurring radioactive isotopes in an LSI circuit may have concentrations
far below the level of practical screening and still affect the circuit reliability. For
example, Polonium is a radioactive element which is widely used in both academia
and industry as a radiation source because it is very cheap and uncontrolled
(in moderate quantities) by government regulations.  Polonium occurs naturally as
a daughter of radon gas and is commonly found in basements and in water pumped
from wells. But a very small amount (far less than one part per billion atoms) can
cause sensitive LSI circuits to upset at rates up to several times per minute.

Another source of energetic particles is galactic and solar cosmic rays. Cosmic rays
are of undetermined origin. They have immense energies and bombard the earth from
all sides. A flux of about 1600/m²-s bombards the earth's outer atmosphere.   Solar
cosmic rays are less energetic and come from the sun.

Neutrons are produced by galactic and solar cosmic rays reacting with the nuclei in
the upper atmosphere. Although most of the primary cosmic rays and the charged
particle component of the cosmic-ray shower are absorbed by the atmosphere,
neutrons, because they have long mean-free paths can penetrate the atmosphere
(equivalent to 13 feet of concrete) and then penetrate through the ceiling into a
multistory building. These neutrons can interact with the atoms of the semiconductor
device and cause charged recoils and alpha particles that deposit charge and energy in
the devices. This charge deposition can initiate SEU in semiconductor devices.
 

OBJECTIVES of the SEU testing:

There are four test objectives:

    1. Obtain the upset cross section curve for linear energy transfers (LET) less than
    15 MeV-cm2 /mg for bias voltage conditions of (defined per application) volts.

    2. Determine if the upset cross section increased significantly for He impacts
    up to 60 degrees off normal incidence.

    3. Measure the upset cross section at LET up to  15 MeV-cm2 /mg to simulate
    silicon ion recoils.

    4. Measure the upset cross section for 20 MeV protons as simulation of
    energetic (>10 MeV) neutrons.
 
 

TYPICAL STATEMENT OF WORK

1. Alpha Sciences (ASI) will supply cables, power supplies, electrical test equipment, and
personnel to operate the equipment and measure the electrical functionality of the
device under test (DUT).  ASI will assist in choosing the radiation test facility
based on test requirements. The tasks to be performed are:

a. ASI will prepare and submit experiment plans and scheduling requests
to comply with the selected radiation facility standard operating procedures.

b. Build the required test fixtures.

c. Measure the pre-irradiation functionality of the customer DUT.

d. ASI will travel to the selected radiation facility and expose the DUT per test plan
and measure the in situ and post-irradiation  functionality of the DUT.

e. ASI will prepare and submit radiation test report.
 

2. Customer will furnish the DUT to be tested.

3. DUT shall be transported to and from the radiation test facility with the
pins in conductive foam rather than under bias.

4. Single Event Effects testing is to be performed in accordance with ASTM
(F1.11) F1192, “Guide for the Measurement of Single Event Phenomena (SEP)
Induced by Heavy Ion Irradiation of Semiconductor Devices.”

5. The test results are to be tabulated in a convenient form and transmitted promptly
via email to the customer The device under test will be returned to customer after the tests.

6. All devices must be handled as ESD (Mil Std 1686, Class I) sensitive.

Please contact Alpha Sciences Inc. to discuss your application
for SEU testing.

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