Effects of humidity on non-hermetically packaged III-V ...
Effects of humidity on non-hermetically packaged III-V structures and devices
Rosa Leon, Suzanne Martin, Tracy Lee, James O. Okuno, Ronald P. Ruiz, Robert E. Gauldin, Michael C. Gaidis and R. Peter Smith
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109
85C 85% humidity test
OH-III 027 ret(5,3) r4c4 type F
85C 85% humidity test
OH-III 027 ret(5,3) r3c2 type B
High humidity and temperature tests (known as 85/85 tests) were performed on various III-V devices and
structures to determine environmental effects in non-hermetically packaged GaAs membrane mixer
diodes. Results are shown for conventional recessed Au/Ge/Ni/Ag/Au ohmic contact test structures, thin
films of AlGaAs and for anode-less and operational 2.5 Terahertz mixer diodes. Performance and
morphological degradation were determined by using four point probe measurements (transmission line
method) for ohmic contacts, by Scanning Electron Microscopy examination and by measuring the DC
Current-Voltage (I-V) characteristics in the membrane diodes. The 85/85 humidity test caused a slight
degradation in the contact resistance of the ohmic contact test structures and an increase in the scatter in
measurements between similar test contact structures. Blistering in various regions of the GaAs
membrane diodes and complete consumption of epitaxial AlGaAs test films were also found. However,
the I-V characteristics of the 2.5 THz membrane-diode mixers did not degrade after 500 hours at 85C
and 85% relative humidity.
R1c3 lh test
R1c3 rh test
R3c2 lh test
r4c4 lh test
Some of the far infrared sensing applications for III-V devices are incompatible with hermetic enclosure of the
sensing device due to the unavailability of non-absorbing window materials. The effects of humidity on
semiconductor devices have shown detrimental effects in the past, from failures due to large increases in
threshold current in InP-based lasers  to mechanical stresses due to polymeric layers volume expansion in
micro-mechanical devices . Humidity in Ag based metallization in microelectronic interconnects has
caused metal corrosion and dendrites due to migration .
Degradation in contact resistance after 100 hours in an 85% humidity environment and 85 degrees. The test
structures consisted of a pad of equal area with varying separation between metallization in GaAs ohmic contacts. This data
is relevant to both the 640 Ghz and 2.5 Thz mixer diodes. The contact resistance for these structures degraded from an
average of 5.16 x 10-6 cm2 to an average of 6.44 x 10-6 cm2, roughly 20%. Second set of data shows more scatter in
values but still shows a statistically significant degradation.
6.7 x 10 (Amps)
2.7 x 10
2.9 x 10
2.5 x 10
1.3 x 10
3.1 x 10
3.6 x 10
6.0 x 10
After 100 hours at 85 C
After 500 hours 85 C and
and 85% relative humidity 85% relative humidity
2.2 x 10
5.4 x 10
1.6 x 10
2.7 x 10
1.3 x 10
4.9 x 10
2.3 x 10
2.1 x 10
Scanning electron micrograph
of 2.5 THz GaAs membrane
diodes and frame prior to
humidity testing. Membranes
are 3 microns thick.
Table 1. Changes in contact resistance (in ohms) after 100, 500 and 1000 hours in 85/85
humidity test. Test pads distributed among 4 GaAs wafer pieces (1 and 3), (4, 5 and 6),
(10, 12, 13 and 14) and (15, 16, 17, 18, 19, 22, 24, 26, 29, 30 and 31). Piece containing
10, 12, 13 and 14 showed some very high contact resistance from some of the pads (not
used in test) and other anomalous behavior.
This study was undertaken with the 2.5 THz GaAs monolithic membrane-diode mixers (fabricated at the Jet
Propulsion Laboratory) to be used on the Earth Observing System Microwave Limb Sounder instrument [4,5].
These devices will be used to measure and differentiate the emission from O 2 at 2502 GHz and OH at 2510 and
2514 GHz (119.820, 119.438 and 119.248 microns respectively). The tests were done to assess any possible
effects from moisture during the pre-launch time period.
Pre-testing IV data
Enlarged view of membrane
without humidity testing.
Blistering in unprotected metallization in
GaAs mixer diodes after 1000 hours at 85 C and
85 % RH.
Enlarged view of blistered area.
AlGaAs is unsuitable for nonhermetic device applications even with a GaAs cap. The
effectiveness of other standard passivating films still remains to be investigated.
2.5 THz GaAs membrane mixer diodes (with unpassivated membrane backs) do not show
degradation in their DC I-V characteristics after 500 hours of 85/85 testing.
Process residues can cause morphological changes (blistering) in exposed areas of GaAs
devices subject to humidity testing.
Gap (in micrometers)
Unpassivated standard recessed Au/Ge/Ni/Ag/Au ohmic contacts on GaAs suffer a slight
degradation in contact resitance (Rs). Values for Rs from different test pads show much greater
variance after the 85/85 tests. Identifying the cause for this variance will require more detailed
structural characterization like transmission electron microscopy or scanning probe microscopy
Poster background shows crater formed in 1.5 micrometers Al 0.98Ga0.02As film capped with a 30 nm GaAs film. Severe film deterioration occurred after 1000 hours in ambient conditions (25 C, ~ 50%
relative humidity). The films that were subjected to 85/85 testing were totally detached from the GaAs substrates and consumed by the resulting oxidation. Crater is ~ 40 micrometers in diameter.
1. J. W. Osenbach, T. L. Evanosky, N. Chand, R. B. Comizzoli, and H. W. Krautter, Temperaturehumidity bias behavior and acceleration factors for nonhermetic uncooled InP-based lasers Journal of
Lightwave Technology, Vol 15, 861 (1997)
2. Buchhold R, Nakladal A, Gerlach G, Sahre K, Eichhorn KJ, Muller M, Reduction of mechanical stress
in micromachined components caused by humidity-induced volume expansion of polymer layers,
MICROSYSTEM TECHNOLOGIES Vol 5, 3 ( 1998
3. R. Manepalli, F. Stepaniak, SA Bidstrup-Allen, and PA Kohl, Silver metallization for advanced
interconnects, IEEE Trans. on Adv. Packaging, Vol 22, 4 (1999)
4. Waters JW et al., The UARS and EOS microwave limb sounder (MLS) experiments, J. Atm. Sci., Vol
56, 194 (1999).
5. Siegel PH, Smith RP, Gaidis MC, Martin SC, 2.5-THz GaAs monolithic membrane-diode mixer IEEE
Trans. on Microwave Theory and Techniques, vol 47, 596 (1999).
6. O. Hallberg and P.S. Peck, Recent humidity accelerations, a base for testing standards, Qual. Reliab.
Eng. Int. Vol 7, 169 (1991).
Poster presented at the 2nd Annual Microelectronics Reliability and
Qualification Workshop, Oct. 26-27, 1999, Pasadena, CA
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