#### Technology Readiness Overview:

##### Reliability of III-V radio frequency (RF) devices

Rosa Leon, Jet Propulsion Laboratory February 2003

**Brief description of RF or MMIC technology**

In RF applications, III-V semiconductors can offer better high frequency
performance. Gallium Arsenide, or GaAs components as they are commonly
called, are particularly useful in the high frequency/high data rate
applications typically used for broadband and radio frequency (RF)
wireless components and of course, several types of satellite
communications. The inherent physical properties of GaAs enable
components based on this material to be four to five times faster than
their traditional silicon competitors. This is because the most
important limitation on the transistors frequency response is the
transit time of minority carriers across the base region, and this
transit time is shorter as the electron mobility is increased.

RF devices are also available from CMOS technology; however, this
overview will focus on higher mobility III-V materials since their much
smaller markets translate into less reliability data and lesser-known
failure and degradation mechanisms. Some of the general advantages of
III-V devices in space applications also include extended thermal ranges
for operation (both hot and cold) and a generally superior radiation
tolerance.

The development of high-frequency wireless applications in the military
and satellite end markets generated the monolithic microwave integrated
circuit (MMIC) and GaAs was found to operate extremely well at microwave
frequencies. These devices are used to receive and transmit signals in a
variety of high-volume communications applications in cellular telephone
systems and personal communication systems, as well as in fiber optic
communication systems, cable, and direct broadcast satellite (DBS).

Technology in the 300 Ghz to 10 terahertz (1 mm-30 µm wavelength) region
of the electromagnetic spectrum is currently experiencing explosive
growth. This growth is fueled largely by need for faster signal
processing and communications, high-resolution spectroscopy, atmospheric
and astrophysical remote sensing, and imaging with unique contrast
requirements.

Recent advances in THz technology include new compact sources of broad
and narrow-band THz radiation, THz receivers with lower noise and higher
bandwidth, and electronic materials engineered for ultra fast carrier
dynamics or enormous optical non-linearities. Active systems for
terahertz imaging with high spectral resolution have been demonstrated
in the laboratory. Terahertz technologies are being explored for wider
bandwidth communications and sensing for satellite systems and upper
atmosphere imagery. More specifically, the objective is the development
of solid-state terahertz devices for operation in the range between 0.3
THz to 10 THz suitable for sources and detectors for use in space-based
communications, atmospheric sensing, and potentially short-range
terrestrial and airborne communications and near object analysis.

Table 1. Bands available for fixed satellite services and other space
applications of microwave radio frequencies.

+---------+-------------------+-------------------+-------------------+
| Radio   | Earth-to-space    | Space-to-earth    | Comments          |
| fr      | frequencies       | frequencies       |                   |
| equency |                   |                   |                   |
| band    |                   |                   |                   |
+---------+-------------------+-------------------+-------------------+
| S-      | 2-4 GHz           | 2-4 GHz           | used for          |
|         |                   |                   | communicating     |
|         |                   |                   | with piloted      |
|         |                   |                   | space missions    |
+---------+-------------------+-------------------+-------------------+
| C-      | 5.850 -- 6.425    | 3.6 -- 4.2 GHz    | Satellite         |
|         | GHz               |                   | communication and |
|         |                   |                   | spacecraft        |
|         |                   |                   | communications on |
|         |                   |                   | Mercury and       |
|         |                   |                   | Gemini flights    |
+---------+-------------------+-------------------+-------------------+
| Ku-     | 12.75 -- 13.25,\  | 10.7 -- 12.75,\   | Satellite         |
|         | 13.75 -- 14.8 GHz | 17.3 -- 17.7 GHz  | communication     |
+---------+-------------------+-------------------+-------------------+
| Ka-     | 27.5 -- 30.0 GHz  | 17.7 -- 21.2 GHz  | Satellite         |
|         |                   |                   | communication     |
|         |                   |                   |                   |
|         |                   |                   | satellite data    |
|         |                   |                   | relay services,   |
|         |                   |                   | inter-connection  |
|         |                   |                   | of satellite.     |
|         |                   |                   | satellites in     |
|         |                   |                   | geostationary     |
|         |                   |                   | orbit (GSO) and   |
|         |                   |                   | over 500 in       |
|         |                   |                   | non-geostationary |
|         |                   |                   | orbits            |
+---------+-------------------+-------------------+-------------------+
| Q/V-    | 47.2 -- 50.2 GHz  | 39.5 -- 42.5 GHz  | Satellite         |
|         |                   |                   | communication     |
+---------+-------------------+-------------------+-------------------+
| W       | 80-110 GHz        | 80-110 GHz        |                   |
+---------+-------------------+-------------------+-------------------+
| Sub     | 300 GHz-10        | (1 mm -- 30       | Atmospheric       |
| mil     | Terahertz         | micron            | sensing and       |
| limeter |                   | wavelength)       | infrared          |
|         |                   |                   | telescopes        |
+---------+-------------------+-------------------+-------------------+

Performance and noise requirements for these novel devices demand
complex geometries and extremely difficult and lengthy fabrication
processes. Frequencies above 1 THz can only be obtained with very thin
membranes suspended on a frame, as shown in Figure 1 or with whisker
contact or planar technologies as shown in Figure 2. Novel Au-plated air
bridges are also needed to reduce stray capacitance and series
resistance. The structural complexity of these fragile devices presents
major reliability concerns in its own right, the demanding use
conditions in space applications increase the need for thorough
reliability testing outside terrestrial applications.

![](media/image1.png)

![](media/image2.png){width="3.0in" height="2.5104166666666665in"}

> Figure 1. Scanning electron micrograph of 2.5 THz GaAs membrane diodes
> and frame prior to humidity testing. Lower micrograph shows detail of
> anode region, placed in the middle of membrane which is 36 microns
> wide, 600 microns long and 3 microns thick.

![](media/image3.png){width="3.29375in" height="2.186111111111111in"}

> Figure 2. Planar Schottky diode from the University of Virginia.
> Planar Schottky diode technology has made significant progress in the
> last few years minimizing extrinsic parasitic loses that limit the
> performance of these devices. These improvements will allow
> integration of these devices into MMIC in the near future.

NASA present and future needs in advanced RF devices

While the present state of technology can accommodate frequencies up to
Q-band, and possibly up to W-band with commercially available devices,
submillimeter wave frequencies can be obtained only from devices still
in research and development stage. Despite the unknowns in the
reliability of these research devices, these are already being used in
space flight, and are essential components of several EOS MLS and also
in various orbiting infrared space telescopes, like Herschel and Planck
(see Table 1).

There are numerous millimeter and submillimeter wave space applications
that require power sources for transmitters, and low noise local
oscillators for receivers and arrays. At the highest frequencies,
GaAs-based solid-state frequency multipliers are employed to efficiently
transfer the output of lower frequency sources to harmonic frequencies.
Nonlinearities in either the I-V or the C-V characteristics of these
devices offer the possibility of frequency multiplication. It is well
known that the power handling capability of familiar low frequency
solid-state devices is relatively low, especially at higher frequencies
(i.e. \> 100 GHz). At frequencies exceeding 250GHz, GaAs-based varactor
multipliers offer the highest solid-state power output, making them
promising candidates as reference local oscillator (LO) sources.
Schottky diode mixers are also showing very promising characteristics
and remain the element of choice as receivers for the shortest
submillimeter wavelengths. A mixer is any device used to multiply
signals that have a nonlinear response to an electric field. Mixers
combine a radio frequency \[RF\] signal and an LO. The result of the
multiplication for two co-sinusoidal signals is then applied to a filter
that only accepts the bandwidth of interest.

GaAs Varactor Multipliers and GaAs Mixer Diodes for Submillimeter and
THz Receivers used in radio astronomy are targeted for very diverse
applications. These range from the detection of naturally-occurring
microwave thermal emission from the limb of Earth\'s atmosphere in
NASA's Micro Limb Sounder instrument, to the future joint NASA/ESA FIRST
mission infrared-submillimeter detection of the dusty galaxies from
which no visible light can escape (the major extragalactic sources in
this wavelength interval). Despite this apparent divergence in
scientific research goals, GaAs based RF devices of almost identical
structure are common reliability concerns in both these missions, and in
several other future and planned applications of submillimeter-wave
radio astronomy.

**Technology Readiness level - readiness for infusion into flight
systems**

RF or MMIC technology could be classified from the point of view of its
readiness for infusion into flight systems according to the technology
readiness level (TRL) scale. Given the diversity in technologies and
applications, this technology spans several TRL levels depending on the
application, the specific structure and device design, and the
manufacturer. Among the higher TRL are devices commercially available
and presently used in communication applications; among the lower TRL
are most of the devices that operate at THz frequencies in radio
astronomy applications.

TRL 4: **Component/subsystem validation in laboratory environment.**
Stand-alone prototyping implementation and test. Integration of
technology elements. Experiments with full-scale problems or data sets.

TRL 5: **System/subsystem validation in relevant environment.** Thorough
testing of prototyping in representative environment. Basic technology
elements integrated with reasonably realistic supporting elements.
Prototyping implementations conform to target environment and
interfaces.

TRL 6: **System/subsystem model or prototyping demonstration in a
relevant end-to-end environment (ground or space)** Prototyping
implementations on full-scale realistic problems. Partially integrated
with existing systems. Limited documentation available. Engineering
feasibility fully demonstrated in actual system application.

TRL 7: **System prototyping demonstration in an operational environment
(ground or space).** System prototyping demonstration in operational
environment. System is at or near scale of the operational system, with
most functions available for demonstration and test. Well integrated
with collateral and ancillary systems. Limited documentation available.

####### Commercial production and manufacturability issues

Because of the cost, demand for high-frequency GaAs chips was confined
to the military radar and satellite applications until the mid 1990's.
As sales to the aerospace industry and military didn\'t build a
high-volume market, manufacturing chips for very specific functions that
cost \$1000 to \$2000 a pop prevented anyone from seriously considering
commercial markets. Another problem was that yields from GaAs wafers
fluctuated quite a bit. Yield refers to the amount of commercially
viable chips that are completed by the end of the manufacturing day
after all the complex process steps have been performed on the wafer.
This variability in yields was one the factors that contributed to GaAs
manufacturer shakeouts throughout the 1980s.

The GaAs companies utilize essentially the same process technology as
the silicon chipmakers. In fact, the majority of their initial
manufacturing facilities were acquired from silicon foundries. The
manufacturing process starts with a pure crystal of GaAs that is
typically grown from seed crystal, which is then sliced into ultra-thin
\"wafers\" with a diamond saw. The wafers are then polished to a flat
mirror finish in anticipation of the deposition of hundreds of circuit
layers. This layer deposition, is called homo-epitaxy for a similar
semiconductor (but a different dopant for example) or hetero-epitaxy,
when slightly different crystal structures are deposited on GaAs.
Examples could be AlGaAs, or strained InGaAs. This deposition can be
achieved with mono-atomic layer control using the techniques of metal
organic chemical vapor deposition (MOCVD) or Molecular beam epitaxy
(MBE).

In the early stages of GaAs development, operators couldn\'t count on
getting wafers that were of uniform shape or size, which made
forecasting for high-volume manufacturing extremely difficult. Yield
crash is still a problem for some manufacturers. This is when yields
decline, for instance, from 50% to 10%, all in a matter of days due to
chemical contamination or a whole host of other problems that have
largely been eliminated when working with silicon.

Over the past couple of decades Gallium Arsenide integrated circuit
technology has overcome many of these performance barriers that hampered
its initial development. It is only recently that the manufacturing
process has matured to the point where high-volume commercially viable
products have been churned out. The GaAs industry has converted from 4
to 6 inch wafers, which will boost yields, but still lags behind in
comparison to their well-endowed brethren in the silicon wafer arena
that use current wafer sizes of 8 inches and moving to 12 inches in the
future. It is estimated that under current conditions 80 silicon chips
can be produced with the same foundry resources required to produce one
Gallium Arsenide device, meaning that GaAs is still limited to
high-performance applications where the performance justifies the cost.
MOCVD processes for multi-wafer 8-inch GaAs substrates have been
demonstrated (Aixtron) already, which reduces this discrepancy in
production yield with Silicon manufacturing.

The markets based on the RF devices with low noise; high power, high
efficiency and working at high frequency are growing and expanding very
quickly. In fact the market experienced a phenomenal growth rate of
200-300% in 1997-1998. The increasing epi-wafer demand drives
manufacturers to build high volume (more than 20,000 wafers/year in the
facility) Molecular Beam Epitaxy (MBE) production systems with low cost
and high device performance.

A new report claims that the compound semiconductor market is now
growing faster than the silicon industry. Consulting firm Kline &
Company (Little Falls, NJ), says its Global Outlook for Chemicals and
Materials in Compound Semiconductors, 2002-2007, that, after waiting in
the wings for more than two decades while silicon put on a strong growth
performance, the time has finally come for compound semiconductors and
that growth will be stronger for these devices than for the logic and
memory devices that rely on silicon technology. In 2001, says the
report, integrated circuits worth about \$119 billion were produced, but
only \$3 billion of this was in the form of compound semiconductors,
while silicon accounted for the rest, but that this imbalance between
silicon and compound semiconductors will soon decrease. The study
focuses on Group IV compounds - mainly silicon-germanium and silicon
carbide - and Group III and Group V elements, including gallium
arsenide, indium phosphide and gallium nitride. Compounds of Group II
and VI elements are also examined.

An important development in III-V manufacturing has been the
introduction of GaAs-on-silicon technology. The technique, pioneered by
Motorola, which is used to form GaAs on top of silicon, utilized an
interstitial layer to absorb the differences in the crystal lattice.
Originally, the team used a perovskite, strontium titanate (STO), to
build ultra-thin transistors. During this work, the researchers
discovered that oxygen tended to leak into the silicon underneath,
forming an amorphous layer. In a silicon transistor, that caused
problems. But Motorola Labs\' Dr Jamal Ramdani thought the effect might
be useful in its own right as a way of putting compound semiconductors
onto a silicon substrate. The amorphous layer allowed the perovskite to
relax to its normal crystal lattice form. By modelling the bonds formed
between GaAs and STO, the team created a recipe for depositing GaAs. IQE
used molecular-beam epitaxy to build the layers up to sufficient
thickness. Since its announcement in September 2001, **Motorola Labs**
has continued to improve the technology and the manufacturing processes,
including the quality and uniformity across large wafers.

###### Available vendors

The main industrial players in the manufacturing of GaAs (and other
III-V) devices for RF applications are **TriQuint**, **Vitesse
Semiconductors**, **Hewlett Packard**, and **Anadigics**. Other
commercial contributors in the manufacture of advanced RF devices are
**Kopin Corporation**, **Motorola Inc**., **RF Micro Devices Inc**.,
**Lockheed Martin Co**., **Honeywell Inc**., **Conexant** (Newport
Beach, CA, USA) and **United Monolithic Semiconductors** (UMS) (from
France). Japanese manufacturers of GaAs based RF devices include
**Toshiba** and **Fujitsu Corp**.

GaAs RF devices can be purchased from several of these vendors. For
example, **[Lockheed Martin Co]{.underline}**. offers MMIC Technology
that includes high Performance and Reliable 60GHz GaAs PHEMT with an
output power as high as 550mW (0.46W/mm) with 23.5% power added
efficiency has been demonstrated and a mean-time-to-failure (MTTF) of
1x10^7^ hours at a channel temperature of 120°C has also been projected
from the MMIC at 60GHz. The developed solid-state power amplifier (SSPA)
technology supports the cross-link applications at V-band.

**[TriQuint Semiconductors]{.underline}** has become larger in the last
few years through acquisitions and partnerships. TriQuint has recently
acquired a substantial portion of Agere's optoelectronic business, which
includes lasers, detectors, modulators, passive components, arrayed
waveguide-based components, amplifiers, transmitters, receivers,
transceivers, transponders, and MEMS (micro electro-mechanical systems).
Following TriQuint's acquisition of Infineons's GaAs business, TriQuint
has also bought IBM SiGe wireless phone chipset business, which is based
on silicon germanium process technology. A recent partnership with
Philips Semiconductors (from Eindhoven, The Netherlands) will certainly
benefit from Philips extensive RF design experience. At the present,
TriQuint is a mass volume manufacturer of GaAs semiconductors, can grow
and design epitaxial layers, and can implement new process developments.

Among its offerings, TriQuint provides the CFY35, a low noise GaAs field
effect transistor that can operate up to 14 Gigahertz. Other available
GaAs RF devices from this company are the CHF120, a GaAs MMIC with HEMT
that operates at up to 18 Gigahertz; the CGY 196, a broad band power
amplifier, the CGB 240B, a 2.4 GHz, 3.3V GaAs MMIC; and a 2-stage InGaP
HBT power amplifier for WLAN and Blue tooth applications with a wide
operating voltage range (2.0 - 5.5 V).

Among the Gallium Arsenide (GaAs) microcircuits developed by
**[Hewlett-Packard]{.underline}**, primarily for use in GPS receivers,
Personal Communications Service, and other wireless RF applications are
several Monolithic Microwave Integrated Circuits (MMICs) which are
small, broadband gain blocks in Surface Mount packages; are relatively
low in noise, and are intended to be used with 50 ohm input and output
impedances. The Model MGA-87563 is a two-stage, low-noise RF amplifier
MMIC, designed for use in the 0.5 to 4 GHz range at a nominal gain of
12.5 dB. The MGA-86563 is a three-stage version, offering higher gain of
typically 21.8 dB.

**RF Micro Devices, Inc.** **RFMD** (Greensboro, NC, USA) recently
introduced its **Polaris Transceiver** which Combines SiGe, CMOS & GaAs
HBT integrated circuits. The transceiver performs all major functions of
the RF section, including both transmit and receive, and provides
handset manufacturers the benefits of reduced component count, flexible
baseband interfaces and lower cost of implementation. The new
transceiver comprises the following components: a SiGe BiCMOS receiver
with three LNAs, polyphase down-converting mixer, bandpass filter and DC
offset correction. The RF6001, which is a CMOS mixed signal processor
with digital channel filters, fractional-N frequency synthesizer,
digital GMSK modulator and integrated power ramp DAC. Finally, the
RF3133 is a GaAs HBT power amplifier module with internal matching
components and integrated closed-loop power controller.**\
Fujitsu Compound Semiconductor, Inc. (FCSI)**, has announced a new 2.5
Gb/s receiver module designed for use in long haul SONET, SDH, and DWDM
systems. The new InGaAs Avalanche Photodiode (APD) detector, FRM5W232BS,
incorporates a GaAs IC transimpedance preamplifier and a thermistor in a
mini-DIL type package. Featuring high sensitivity at -34 dBm (typical)
and a high differential electrical output, this device contains a
nominal 10-kohm integral thermistor that allows accurate monitoring of
the APD temperature and facilitates the design of the APD bias control
circuits. The integrated transimpedance amplifier is designed with the
standard power supply of +3.3 V resulting in low power consumption (0.15
W).

**Toshiba America Electronic Components**, (IRVINE, California) has
announced the industry\'s first 60 watt internally matched C-Band
gallium arsenide field effect transistor (GaAs FET) designed to support
extended C-Band satellite communications. The TIM5964-60SL-251, which
operates in the 5.9 to 6.75 gigahertz (GHz) range, is targeted for use
in solid-state power amplifiers (SSPA) for gateway or earth-station
satellite communications (SATCOM), very small aperture terminals (VSAT),
and for long-haul, point-to-point terrestrial communications. The device
increases the maximum output power of the amplifiers within existing
design platforms, and allows designers to use a single transistor for
all satellite communications designs in the extended C-Band range. By
supporting a broader frequency range than the standard C-Band (5.9 to
6.4 GHz), TAEC\'s C-Band GaAs FETs help simplify satellite
communications design. A shortage of C-Band satellite network traffic
capacity has developed as a result of increased multimedia content, and
additional frequency in the Palapa SAT range (6.425 to 6.725 GHz) has
been used to meet the growing demand for capacity.

**Motorola** Broadband Communications Sector has introduced the Motorola
SG900 - Weighing in at 7.5 pounds, the SG900 is the company\'s smallest
single-output optical node and features 870 MHz forward band pass, an
integrated optical receiver, and uses Motorola\'s Gallium Arsenide
(GaAs) Hybrid Technology.

**ANADIGICS Inc** (Warren, NJ, USA) is sampling the AWT6200 PowerPlexer,
the first in a new family of integrated RF modules for class-12 capable
GPRS performance for dual-band GSM/DCS wireless handsets. It integrates
6\" InGaP HBT power amplifiers (enabling maximum talk and stand-by
time), GaAs pHEMT multi-throw RF antenna switch (ensuring voice/data
quality and improved signal strength) as well as passive filters
integrated passives and analog control ICs in a small module package.
**ANADIGICS** also offers the AWT6109 InGaP HBT-based 3.5 V
high-efficiency, linear, power amplifier module optimized for use in
Korean Band PCS CDMA handsets and the 250-3000 MHz AGB3300 50 W GaAs
high-linearity gain block amplifier (housed in a small SOT-89 surface
mount package) for transmit and receive paths in wireless infrastructure
equipment (W-CDMA, CDMA, TDMA, GSM, PCS, PHS, Bluetooth, WLL, 802.11b
and MMDS). **ANADIGICS** is also shipping production volumes of a power
amplifier chipset (two power amplifiers and amplifier driver) for
**Ericsson**\'s new R300d WAP-enabled tri-mode phone.

**Raytheon** Company\'s (Andover, MA, USA) RF Components Division has
launched the RMLA00400 transimpedance amplifier (TIA) for 40 Gb/s
(OC768) fibre-optic systems, available in die form (3.71mm x 1.70mm
chip) and made using its 4\" GaAs-based MHEMT process technology. Key
features include a high bandwidth of 40 GHz, low group delay and low
power dissipation of 450 mW.

**Kopin Corp** (Taunton, MA, USA) is supplying InGaP HBTs (with fT = 190
GHz and fmax = 230 GHz) to **Yokogawa Electric Corp** (Tokyo, Japan) for
integration into its 40 Gb/s optical network modules (the world\'s first
to use InGaP HBTs for OC-768). **Yokogawa** has released an entire
family of OC-768 modules based on the InGaP HBT platform, including
driver modules for lithium niobate and electro-absorption modulators, as
well as logic circuit modules for multiplexer, demultiplexer and
flip-flop functions.

**General reliability and radiation concerns:**

The simplest definition of reliability is quality over time. Since time
is involved in reliability, it is often measured by a rate. Just as
quality is usually measured in terms of rejects (or un-quality),
reliability is measured in terms of failures (or un-reliability).

Traditionally, the measurement of electronic failures has been
straightforward. If one assumes all failure rates are constant, as they
might be in a large system or machine, then a MEAN time between failures
(MTBF) would be expected. In contrast, most integrated circuits,
including GaAs devices, follow the lognormal distribution, which rarely
approximates a constant rate.

Historically, failure rates were measured in percent failed per thousand
hours of operation. The modern unit of failure commonly used today is
failure-in-time (FIT). A FIT is also a unit of failure (or a Failure IT)
that is equivalent to one failure per billion device hours. For
comparison, one FIT is equivalent to 0.0001% per thousand hours, and 1%
per thousand hours is equivalent to 10,000 FIT. However, a single rate
is not sufficient to describe the reliability of semiconductors since
their failure rates change over their lifetimes.

Generally, semiconductors have a very low wear-out failure rate early in
life, and then have increasing failure rates as they wear out. At a
point when about half of the devices fail in a group of circuits, the
failure rate begins decreasing again. A very small part of an IC\'s
population may fail early in life. These early failures have been
associated with manufacturing or assembly defects. The early failures
are sometimes called \"infant\" failures. As semiconductor reliability
improves and more samples are stressed, the early failures become easier
to detect and eliminate.

Failure mechanisms in GaAs device technologies can be significantly
different than those observed for traditional Si devices. First of all,
the metallization used is primarily composed of Gold, which is more
conductive than aluminum used in conventional silicon device processing,
and is also less susceptible to electromigration (electromigration is a
diffusion process, diffusivity scales with melting point and Gold's
melting point is much higher than Aluminum). Gold can also be less
susceptible to corrosion than Aluminum. Lastly, Gold eliminates the
potential for Au/Al intermetallic problems during assembly since Gold
bond wires are typically available.

Secondly, the active device used in mature GaAs ICs is the MESFET.
Unlike a Si MOSFET, the gate is formed by a Schottky metal contact to
the channel, instead of using a gate oxide. This eliminates the primary
failure mechanisms found in MOS devices. Because of this Schottky
configuration, the MESFET is relatively immune to surface effects and
ionic contamination which plague silicon devices. In addition, GaAs
devices are not susceptible to radiation degradation caused by the
sensitivity of gate oxides in Si CMOS devices. Newer GaAs active
devices, pHEMTs and HBTs, also have advantages over MOS devices and
similar immunity to typical silicon surface problems.

The last major component of the process is the bulk wafer material
itself. GaAs is actually a semi-insulator except in areas where it is
implanted with silicon or in epitaxial layers. Because of its higher
bulk resistivity, roughly 1000 times more resistive than silicon, GaAs
is much less sensitive to the isolation and latch-up problems associated
with silicon and silicon CMOS. There are other GaAs properties that lend
themselves to better reliability, like lower electric fields at peak
electron velocity, but they are minor compared to the major groups that
have been discussed.

Common failure mechanisms in GaAs based devices

**Interdiffusion mechanisms**

The primary failure mechanism for MESFET pHEMT ICs and HBTs are
\"sinking gates.\" Sinking gates are caused by gate metal interdiffusion
into the channel. This interdiffusion causes parametric shifts in
several device parameters because the effective channel thickness is
reduced. The largest change is decreased channel current so that
parameter is typically used as the failure criterion. A 20% change in
channel current is a common definition of a MESFET failure. In addition
to channel current changes in an FET with sinking gates, channel
resistance increases and the magnitude of the voltage required to
pinch-off an FET is reduced (this usually means pinch offs are more
positive). Sinking gates have never been catastrophic and they are
self-limiting in a sense, because as the channel current decreases so
does the power in the FET and thus the temperature is lowered causing
the gates to sink more slowly. Eventually, one could expect the channel
to be severed completely by the gate and become open, but this condition
is rarely reached. The sinking gate mechanism has been observed at
various temperatures and biases, but degradation is accelerated by
temperature without bias or RF drive.

Gate degradation can be observed using cross-sections formed with a
Focused Ion Beam (FIB). The movement of the metal gate at the GaAs
surface is dramatic after high temperature aging. Some metal voiding is
also present in the degraded gate, because of the mass of material that
has moved into the GaAs. Operation at the maximum rated temperature
(150°C) would be expected to exceed 2,000 years before a 1dB change
could be observed. This expected longevity of sinking gates is
acceptable in terms of commercial reliability goals, and is not
considered as a threat to device lifetimes under normal operating
conditions. Although gate sinking can be induced by high temperature
acceleration, it has not yet been observed under nominal use conditions.

The failure mechanism for first layer interconnect begins with an
interdiffusion mechanism. The interconnect is composed of a layered
structure of titanium, platinum, and gold. When these metals
interdiffuse, the resistance of the interconnect increases. Auger
studies indicate that the metals intermix, and the whole stack becomes
homogeneous. On a percentage basis, the resistance change can be as high
as 250%. But on an absolute basis, a 50% change is roughly as much as
the process window is wide, or 40 milli-ohms per square cm.

Implanted resistors have been studied to evaluate Ohmic contact failure
mechanisms, but Ohmic degradation mechanisms have been elusive.
Implanted resistor degradation has been found to be caused by changes in
the contact resistance. Failure analysis on degraded FETs has shown that
Ohmic metal does diffuse into the GaAs, but the physical diffusion seems
to have a minimal effect electrically on the FET performance, especially
compared to sinking gates. In general, Ohmic annealing is beneficial to
circuit performance.

**Electrostatic discharge failures**

Electrostatic Discharge (ESD) has been the leading cause of failure in
the field, and ESD failures scale inversely with device size. Therefore,
efforts to reduce ESD sensitivity by design and handling countermeasures
will become increasingly more important as device sizes continue to
decrease.

The problem is difficult to model and analyze since the various sources
of electrostatic energy---such as the human body, testing equipment, and
accumulated free charge---all have different electrical characteristics.
In addition, the abrupt and intense nature of a typical ESD event forces
the devices that absorb the discharged energy to operate under high
injection conditions, where the analysis is quite complex. Providing
adequate protection against ESD also requires effective thermal
distribution within the discharge area in order to avoid either
dielectric damage, semiconductor melting, or metal spiking. To address
these issues appropriately, each pad must be protected by a device
capable of sustaining the discharged energy with no internal damage,
preferably without compromising process complexity, total chip size, and
electrical performance.

**Electromigration**

While metal/semiconductor interdiffusion is the most common wear out
mechanism, and it occurs in GaAs contacts, interconnects, and resistors,
electromigration is another common failure mechanism, and it also occurs
in interconnects and resistors. If life testing is conducted under bias,
electromigration can eventually occur, which causes catastrophic open
circuits.

The failure mechanism for plated gold interconnect and air bridges in
MMICs is electromigration (See illustration of air bridges in an InP RF
device in figure 3). Under high current density stress, mass transport
occurs because of the \"electron wind\" in the metallization. Voids form
along the plated gold, and eventually the interconnect fuses open, the
nitride passivation will crack, and molten gold will flow out of the
failure site. Less than a 25% change in plated gold resistance has ever
been observed before the catastrophic failure, and usually the
pre-fusing degradation is negligible.

![](media/image4.png){width="2.626388888888889in"
height="2.084722222222222in"}

> Figure 3. InP Heterostructure Barrier Varactor (HBV) that utilizes air
> bridges to minimize losses due to extrinsic resistance.

**Other failure modes**

The failure mechanisms for capacitors is Time Dependent Dielectric
Breakdown (TDDB). Many tests have been conducted to evaluate dielectric
performance. After the capacitor dielectric was changed to plasma
deposited nitride in 1985, lifetest failures were non-existent. As the
capacitor dielectric thickness was reduced from 2000 angstroms to 500
angstroms, voltage acceleration testing became more and more effective.
Several improvement efforts have reduced the defect density in
capacitors and they are now approaching theoretical maximums for voltage
breakdown and longevity under voltage stress.

Other possible (less common) failure mechanisms are surface charge
effects, leakage effects, ohmic contact degradation, burn-out, channel
compensation, Schottky contact degradation, carrier diffusion, substrate
via cracking, sidegating, gate electromigration, passivation cracking,
interconnect-airbridge contact degradation, hydrogen-gate
interdiffusion, capacitor dielectric breakdown, interlevel dielectric
breakdown, and Ohmic contact electromigration.

Specific concerns in Space applications:

######### Hot electron effects

Another important degradation and failure mechanism that was not
discussed in the previous section is the hot electron degradation
effect, which is particularly important in the use of III-V devices
under cryogenic conditions. The traditional temperature acceleration in
life testing is more commonly used to predict reliability of GaAs
devices, by simply evaluating experimentally the activation energy and
then substituting actual use conditions into the Arrhenius equation. The
problem with temperature-accelerated stress experiments is that
activation energies for GaAs tend to be quite high, and extrapolation to
use conditions can give values for predicted meant time to failure that
are too optimistic. One of the reasons is that thermally induced
degradation is based on interdiffusion of the different materials
involved, and this depends on temperature and not so much on bias
conditions. On the other hand, a high-bias stress which is related to
the hot electron instabilities in the channel, may present a worse case
scenario when devices are operated at room or low temperatures in a real
environment for a long time period. Such phenomena have been attributed
to the formation of deep level defects generated during hot electron and
impact ionization conditions. These are caused by the presence of large
electric fields in the device channels and barrier layers. Hot electron
effects are quite likely to develop in RF applications (mainly in high
electron mobility transistors HEMTs) because in order to be operated at
microwave and millimeter wave frequencies the peak channel electric
fields are very large even for low drain biases. Hot electron
degradation has been shown to cause threshold voltage shifts, breakdown
walk out, transconductance and cutoff frequency degradation, and the so
called "power slump".

######### Other reliability concerns specific to space applications

Some of the unique space requirements for these devices demand
reliability for five years of operation at temperatures near 80 Kelvin.
As some of these GaAs amplifiers will be routinely expected to provide
in excess of 100mW of power, large thermal gradients are likely to add
an additional concern in device reliability. Further concerns include
the inherent lack of hermeticity. Due to the lack of availability of a
non-absorbing window material many of these devices do not operate under
hermetically sealed conditions. They are assembled in a block, which has
an opening for collecting the signal. Environmental degradation of GaAs
and GaAs metallization is then also a relevant study to be included, and
it is important to simulate pre-launch storage conditions.

> Table 2. Space reliability of Compound semiconductor Transistors (most
> based on GaAs).

+------+------+-----+--------+------+-------+------+------+-------+
| > ** | **S  | *   | **     | **De | **O   | **Ea | *    | **    |
| Spec | EU** | *TI | Displa | vice | perat | from | *ESD | Other |
| ific |      | D** | cement | p    | ing** | life | cla  | inf   |
| >    |      |     | da     | aram |       | tes  | ss** | ormat |
| devi |      |     | mage** | eter | **th  | ting |      | ion** |
| ce** |      |     |        | mon  | ermal | (or  |      |       |
|      |      |     |        | itor | range | expe |      |       |
|      |      |     |        | ed** | a     | cted |      |       |
|      |      |     |        |      | nd/or | mean |      |       |
|      |      |     |        |      | elect | time |      |       |
|      |      |     |        |      | rical | to   |      |       |
|      |      |     |        |      | str   | fa   |      |       |
|      |      |     |        |      | ess** | ilur |      |       |
|      |      |     |        |      |       | e)** |      |       |
+------+------+-----+--------+------+-------+------+------+-------+
| C-HI | LET  |     |        | Bit  | > 5 K |      |      |       |
| GFET | \>   |     |        | e    | > to  |      |      |       |
| C    | 90   |     |        | rror | > 400 |      |      |       |
| ompl | Me   |     |        | cr   | > K   |      |      |       |
| emen | V.cm |     |        | oss- |       |      |      |       |
| tary | 2/mg |     |        | sect |       |      |      |       |
| het  | sev  |     |        | ions |       |      |      |       |
| eros | eral |     |        | u    |       |      |      |       |
| truc | ions |     |        | nder |       |      |      |       |
| ture |      |     |        | dyn  |       |      |      |       |
| i    | >    |     |        | amic |       |      |      |       |
| nsul |  Ref |     |        | co   |       |      |      |       |
| ated | > \  |     |        | ndit |       |      |      |       |
| gate | [1\] |     |        | ions |       |      |      |       |
| FET- |      |     |        |      |       |      |      |       |
| 1k   |      |     |        |      |       |      |      |       |
| SRAM |      |     |        |      |       |      |      |       |
+------+------+-----+--------+------+-------+------+------+-------+
| A    |      |     | 40 MeV | Drai |       |      |      | > GaN |
| lGaN |      |     | pr     | n-so |       |      |      | >     |
| /GaN |      |     | otons, | urce |       |      |      | based |
| H    |      |     | f      | cur  |       |      |      | > de  |
| EMTs |      |     | luence | rent |       |      |      | vice, |
| (    |      |     | up to  | vs   |       |      |      | > in  |
| high |      |     | 5 x    | drai |       |      |      | >     |
| elec |      |     | 10^10^ | n-so |       |      |      |  opto |
| tron |      |     | cm^-2^ | urce |       |      |      | elect |
| mobi |      |     | -- max | volt |       |      |      | ronic |
| lity |      |     | fre    | age, |       |      |      | > ap  |
| tran |      |     | quency | gate |       |      |      | plica |
| sist |      |     | of     | curr |       |      |      | tions |
| ors) |      |     | oscil  | ent, |       |      |      | >     |
|      |      |     | lation | rev  |       |      |      |  they |
|      |      |     | c      | erse |       |      |      | > are |
|      |      |     | hanged | br   |       |      |      | > 1   |
|      |      |     | by 5   | eakd |       |      |      | order |
|      |      |     | to 25% | own, |       |      |      | > of  |
|      |      |     | \[11\] | max  |       |      |      | >     |
|      |      |     |        | imum |       |      |      |  magn |
|      |      |     |        | f    |       |      |      | itude |
|      |      |     |        | requ |       |      |      | > h   |
|      |      |     |        | ency |       |      |      | arder |
|      |      |     |        | of   |       |      |      | >     |
|      |      |     |        | osci |       |      |      |  than |
|      |      |     |        | llat |       |      |      | >     |
|      |      |     |        | ion. |       |      |      | GaAs. |
+------+------+-----+--------+------+-------+------+------+-------+
| In   |      |     |        | Tran |       | E    |      |       |
| AlAs |      |     |        | scon |       | a=1. |      |       |
| /InG |      |     |        | duct |       | 8eV, |      |       |
| aAs? |      |     |        | ance |       | MTT  |      |       |
| GaAs |      |     |        | deg  |       | F=2x |      |       |
| H    |      |     |        | rada |       | 107h |      |       |
| EMTs |      |     |        | tion |       | at   |      |       |
|      |      |     |        | (    |       | Tch= |      |       |
|      |      |     |        | used |       | 125C |      |       |
|      |      |     |        | 10%  |       | and  |      |       |
|      |      |     |        | to   |       | Jd=  |      |       |
|      |      |     |        | get  |       | 200m |      |       |
|      |      |     |        | A    |       | A/mm |      |       |
|      |      |     |        | rrhe |       | \[   |      |       |
|      |      |     |        | nius |       | 20\] |      |       |
|      |      |     |        | p    |       |      |      |       |
|      |      |     |        | lots |       |      |      |       |
|      |      |     |        | in   |       |      |      |       |
|      |      |     |        | \[20 |       |      |      |       |
|      |      |     |        | \]). |       |      |      |       |
+------+------+-----+--------+------+-------+------+------+-------+
| A    |      |     |        | Gate | As    | Ea   |      | C     |
| lGaA |      |     |        | curr | high  | is   |      | hange |
| s/In |      |     |        | ent, | as    | assu |      | in RF |
| GaAs |      |     |        | p    | 250ºC | med, |      | inse  |
| p    |      |     |        | inch | (will | MTTF |      | rtion |
| seud |      |     |        | -off | last  | e    |      | loss  |
| omor |      |     |        | volt | \>    | stim |      | was   |
| phic |      |     |        | age, | 9,000 | ated |      | \<    |
| high |      |     |        | cha  | hours | to   |      | 0.1   |
| elec |      |     |        | nnel | at    | be   |      | dB or |
| tron |      |     |        | on   | this  | 1    |      | \< 2% |
| mobi |      |     |        | -res | te    | 0^8^ |      | d     |
| lity |      |     |        | ista | mpera | h    |      | egrad |
| tra  |      |     |        | nce, | ture) | ours |      | ation |
| nsis |      |     |        | d    |       | at   |      | in    |
| tors |      |     |        | rain |       | 50ºC |      | power |
| (PHE |      |     |        | sa   |       | \    |      | loss- |
| MTs) |      |     |        | tura |       | [2\] |      | Pr    |
| used |      |     |        | tion |       |      |      | imary |
| for  |      |     |        | cur  |       |      |      | Fa    |
| high |      |     |        | rent |       |      |      | ilure |
| s    |      |     |        |      |       |      |      | mech  |
| peed |      |     |        |      |       |      |      | anism |
| swit |      |     |        |      |       |      |      | is    |
| ches |      |     |        |      |       |      |      | gate  |
|      |      |     |        |      |       |      |      | si    |
|      |      |     |        |      |       |      |      | nking |
+------+------+-----+--------+------+-------+------+------+-------+
| H    |      |     | Trans  | Vari | They  | On-g | \<1  | De    |
| FETs |      |     | istors | ous: | "     | oing | for  | vices |
| (he  |      |     | were   | t    | work" | life | isol | work  |
| tero |      |     | still  | rans | from  | tes  | ated | over  |
| junc |      |     | func   | cond | 4 K   | ting | dev  | a     |
| tion |      |     | tional | ucta | \[7\] | at   | ices | wide  |
| f    |      |     | after  | nce, | up to | JPL  | \[   | t     |
| ield |      |     | 5 x    | t    | 400ºC | i    | 10\] | emper |
| ef   |      |     | 10     | hres | (673  | ndic |      | ature |
| fect |      |     | ^14^ - | hold | K)    | ates |      | r     |
| tran |      |     | 24 GeV | volt | \     | less |      | ange, |
| sist |      |     | p      | age, | [8\], | than |      | how   |
| ors) |      |     | rotons | d    | how   | 5%   |      | ever, |
|      |      |     | -- Vth | rain | ever, | deg  |      | d     |
|      |      |     | s      | sa   | there | rada |      | evice |
|      |      |     | hifter | tura | is an | tion |      | chara |
|      |      |     | from   | tion | e     | in   |      | cteri |
|      |      |     | 75 to  | cur  | xpone | rev  |      | stics |
|      |      |     | 120    | rent | ntial | erse |      | do    |
|      |      |     | mV,    | (    | inc   | sa   |      | c     |
|      |      |     | 10-5%  | gate | rease | tura |      | hange |
|      |      |     | de     | body | in    | tion |      | with  |
|      |      |     | crease | l    | gate  | cur  |      | te    |
|      |      |     | in     | eaka | body  | rent |      | mpera |
|      |      |     | tran   | ge), | le    | a    |      | ture, |
|      |      |     | scondu | d    | akage | fter |      | requ  |
|      |      |     | ctance | rain | and   | 1000 |      | iring |
|      |      |     | \[9\]  | curr | in    | h    |      | c     |
|      |      |     |        | ent. | drain | ours |      | harac |
|      |      |     |        |      | cur   | at   |      | teriz |
|      |      |     |        |      | rent. | 2    |      | ation |
|      |      |     |        |      |       | 40ºC |      | at    |
|      |      |     |        |      |       | \[   |      | the   |
|      |      |     |        |      |       | 10\] |      | de    |
|      |      |     |        |      |       |      |      | sired |
|      |      |     |        |      |       |      |      | use   |
|      |      |     |        |      |       |      |      | T.    |
+------+------+-----+--------+------+-------+------+------+-------+
| MESF |      | >   |        | >    |       |      |      | >     |
| ETs, |      | Co^ |        | Vari |       |      |      |  Thre |
| MOD  |      | 60^ |        | ous: |       |      |      | shold |
| FET, |      | >   |        | > t  |       |      |      | > vo  |
| N    |      |  at |        | rans |       |      |      | ltage |
| and  |      | > d |        | cond |       |      |      | >     |
| P    |      | ose |        | ucta |       |      |      | shift |
| HIG  |      | > r |        | nce, |       |      |      | > r   |
| FETs |      | ate |        | > t  |       |      |      | anged |
|      |      | >   |        | hres |       |      |      | >     |
|      |      |  10 |        | hold |       |      |      |  from |
|      |      | ^6^ |        | >    |       |      |      | > 5   |
|      |      | >   |        | volt |       |      |      | > to  |
|      |      |  ra |        | age, |       |      |      | > 14  |
|      |      | ds/ |        | > sa |       |      |      | > mV  |
|      |      | hr. |        | tura |       |      |      | >     |
|      |      | >   |        | tion |       |      |      |  depe |
|      |      |  Af |        | >    |       |      |      | nding |
|      |      | ter |        |  cur |       |      |      | > on  |
|      |      | >   |        | rent |       |      |      | > d   |
|      |      |  80 |        |      |       |      |      | evice |
|      |      | >   |        |      |       |      |      | >     |
|      |      | Mra |        |      |       |      |      | type. |
|      |      | ds, |        |      |       |      |      |       |
|      |      | > t |        |      |       |      |      |       |
|      |      | ran |        |      |       |      |      |       |
|      |      | sco |        |      |       |      |      |       |
|      |      | ndu |        |      |       |      |      |       |
|      |      | cta |        |      |       |      |      |       |
|      |      | nce |        |      |       |      |      |       |
|      |      | >   |        |      |       |      |      |       |
|      |      |  de |        |      |       |      |      |       |
|      |      | gra |        |      |       |      |      |       |
|      |      | ded |        |      |       |      |      |       |
|      |      | > o |        |      |       |      |      |       |
|      |      | nly |        |      |       |      |      |       |
|      |      | >   |        |      |       |      |      |       |
|      |      |  2. |        |      |       |      |      |       |
|      |      | 3%, |        |      |       |      |      |       |
|      |      | >   |        |      |       |      |      |       |
|      |      |  dr |        |      |       |      |      |       |
|      |      | ain |        |      |       |      |      |       |
|      |      | > s |        |      |       |      |      |       |
|      |      | atu |        |      |       |      |      |       |
|      |      | rat |        |      |       |      |      |       |
|      |      | ion |        |      |       |      |      |       |
|      |      | > c |        |      |       |      |      |       |
|      |      | urr |        |      |       |      |      |       |
|      |      | ent |        |      |       |      |      |       |
|      |      | >   |        |      |       |      |      |       |
|      |      | inc |        |      |       |      |      |       |
|      |      | rea |        |      |       |      |      |       |
|      |      | sed |        |      |       |      |      |       |
|      |      | > o |        |      |       |      |      |       |
|      |      | nly |        |      |       |      |      |       |
|      |      | > 5 |        |      |       |      |      |       |
|      |      | .5% |        |      |       |      |      |       |
|      |      | >   |        |      |       |      |      |       |
|      |      |  \[ |        |      |       |      |      |       |
|      |      | 6\] |        |      |       |      |      |       |
+------+------+-----+--------+------+-------+------+------+-------+
| HBT  |      |     |        | > RF | > Up  | Ea = |      | >     |
| (het |      |     |        | > ou | > to  | 1.   |      |  Most |
| eros |      |     |        | tput | >     | 75eV |      | > m   |
| truc |      |     |        | > p  |  218\ | life |      | ature |
| ture |      |     |        | ower | > C   | t    |      | >     |
| bip  |      |     |        | >    | > jun | ests |      | techn |
| olar |      |     |        |  and | ction | ext  |      | ology |
| tra  |      |     |        | >    | > t   | rapo |      | > in  |
| nsis |      |     |        |  cur | emper | late |      | > the |
| tor) |      |     |        | rent | ature | MTTF |      | > HBT |
| AlG  |      |     |        | > g  | > \[  | =    |      | > fa  |
| aAs/ |      |     |        | ain, | 16\]. | 1.5  |      | mily. |
| GaAs |      |     |        | > c  |       | x    |      | > S   |
|      |      |     |        | olle |       | 1    |      | trong |
|      |      |     |        | ctor |       | 0^8^ |      | >     |
|      |      |     |        | >    |       | h at |      | depen |
|      |      |     |        | curr |       | junc |      | dence |
|      |      |     |        | ent. |       | tion |      | > of  |
|      |      |     |        |      |       | T =  |      | > d   |
|      |      |     |        |      |       | 1    |      | egrad |
|      |      |     |        |      |       | 25ºC |      | ation |
|      |      |     |        |      |       | and  |      | > on  |
|      |      |     |        |      |       | Jc   |      | > ele |
|      |      |     |        |      |       | =3kA |      | ctric |
|      |      |     |        |      |       | /cm2 |      | >     |
|      |      |     |        |      |       | \[   |      | field |
|      |      |     |        |      |       | 15\] |      | >     |
|      |      |     |        |      |       |      |      |  (not |
|      |      |     |        |      |       | Sepa |      | >     |
|      |      |     |        |      |       | rate |      |  just |
|      |      |     |        |      |       | t    |      | > tem |
|      |      |     |        |      |       | ests |      | perat |
|      |      |     |        |      |       | p    |      | ure). |
|      |      |     |        |      |       | erfo |      |       |
|      |      |     |        |      |       | rmed |      |       |
|      |      |     |        |      |       | at   |      |       |
|      |      |     |        |      |       | 26   |      |       |
|      |      |     |        |      |       | kA   |      |       |
|      |      |     |        |      |       | /cm2 |      |       |
|      |      |     |        |      |       | f    |      |       |
|      |      |     |        |      |       | ound |      |       |
|      |      |     |        |      |       | E    |      |       |
|      |      |     |        |      |       | a=0. |      |       |
|      |      |     |        |      |       | 42eV |      |       |
|      |      |     |        |      |       | with |      |       |
|      |      |     |        |      |       | MTTF |      |       |
|      |      |     |        |      |       | of   |      |       |
|      |      |     |        |      |       | 2020 |      |       |
|      |      |     |        |      |       | h at |      |       |
|      |      |     |        |      |       | junc |      |       |
|      |      |     |        |      |       | tion |      |       |
|      |      |     |        |      |       | T=2  |      |       |
|      |      |     |        |      |       | 18ºC |      |       |
|      |      |     |        |      |       | (c   |      |       |
|      |      |     |        |      |       | orre |      |       |
|      |      |     |        |      |       | spon |      |       |
|      |      |     |        |      |       | ding |      |       |
|      |      |     |        |      |       | to   |      |       |
|      |      |     |        |      |       | base |      |       |
|      |      |     |        |      |       | p    |      |       |
|      |      |     |        |      |       | late |      |       |
|      |      |     |        |      |       | T=1  |      |       |
|      |      |     |        |      |       | 10ºC |      |       |
|      |      |     |        |      |       | \[   |      |       |
|      |      |     |        |      |       | 16\] |      |       |
+------+------+-----+--------+------+-------+------+------+-------+
| In   |      |     |        | >    |       | >    |      | > R   |
| GaP/ |      |     |        |  Cur |       |  Ea= |      | eliab |
| GaAs |      |     |        | rent |       | >    |      | ility |
| HBTs |      |     |        | >    |       | 2eV, |      | > is  |
|      |      |     |        | gain |       | >    |      | > str |
|      |      |     |        | > (b |       | MTTF |      | ongly |
|      |      |     |        | eta) |       | >    |      | >     |
|      |      |     |        |      |       |  106 |      |  depe |
|      |      |     |        |      |       | > h  |      | ndent |
|      |      |     |        |      |       | > at |      | > on  |
|      |      |     |        |      |       | >    |      | > f   |
|      |      |     |        |      |       | junc |      | abric |
|      |      |     |        |      |       | tion |      | ation |
|      |      |     |        |      |       | > T= |      | >     |
|      |      |     |        |      |       | 200C |      | proce |
|      |      |     |        |      |       | >    |      | sses, |
|      |      |     |        |      |       |  and |      | >     |
|      |      |     |        |      |       | > J= |      |  diff |
|      |      |     |        |      |       | 60kA |      | erent |
|      |      |     |        |      |       | /cm2 |      | > st  |
|      |      |     |        |      |       | > \[ |      | udies |
|      |      |     |        |      |       | 17\] |      | >     |
|      |      |     |        |      |       | >    |      |  find |
|      |      |     |        |      |       | >    |      | > w   |
|      |      |     |        |      |       | Sepa |      | idely |
|      |      |     |        |      |       | rate |      | >     |
|      |      |     |        |      |       | > s  |      |  diff |
|      |      |     |        |      |       | tudy |      | ering |
|      |      |     |        |      |       | > f  |      | >     |
|      |      |     |        |      |       | ound |      |  pred |
|      |      |     |        |      |       | >    |      | icted |
|      |      |     |        |      |       | Ea=0 |      | >     |
|      |      |     |        |      |       | .7eV |      |  MTTF |
|      |      |     |        |      |       | >    |      |       |
|      |      |     |        |      |       |  for |      |       |
|      |      |     |        |      |       | > J= |      |       |
|      |      |     |        |      |       | 50kA |      |       |
|      |      |     |        |      |       | /cm2 |      |       |
|      |      |     |        |      |       | > \[ |      |       |
|      |      |     |        |      |       | 18\] |      |       |
+------+------+-----+--------+------+-------+------+------+-------+

**InP RF devices:**

InP based devices are of interest in space applications mainly for
communications, and include digital and mixed signal. InP devices have
also demonstrated superior radiation tolerance to similar GaAs devices.
Some of the advantages of this material for devices related to aerospace
technologies include ultra high speeds (over 100 GHz), low phase noise,
good thermal conductivity, and very good radiation hardness.

> Table 3. Space reliability in InP devices (or using InP substrates):

+--------+--------+--------+--------+--------+--------+--------+--------+
| > **Sp | *      | *      | **     | **     | *      | **Ea   | *      |
| ecific | *SEU** | *TID** | Displa | Device | *Opera | from   | *Other |
| > de   |        |        | cement | par    | ting** | life   | i      |
| vice** |        |        | da     | ameter |        | t      | nforma |
|        |        |        | mage** | monit  | **t    | esting | tion** |
|        |        |        |        | ored** | hermal | (or    |        |
|        |        |        |        |        | range  | ex     |        |
|        |        |        |        |        | and/or | pected |        |
|        |        |        |        |        | elec   | mean   |        |
|        |        |        |        |        | trical | time   |        |
|        |        |        |        |        | st     | to     |        |
|        |        |        |        |        | ress** | fail   |        |
|        |        |        |        |        |        | ure)** |        |
+--------+--------+--------+--------+--------+--------+--------+--------+
| > InP  |        |        |        | 10%    | Up to  | For    | High   |
| >      |        |        |        | degra  | 2V     | Vd= 1  | fre    |
|  based |        |        |        | dation | drain  | V, Ea  | quency |
| >      |        |        |        | in     | v      | =      | perfo  |
|  HEMTs |        |        |        | tran   | oltage | 1.8eV, | rmance |
| >      |        |        |        | scondu | (Vd)   | pro    | is     |
|  (high |        |        |        | ctance | \[12\] | jected | inc    |
| > el   |        |        |        | for    |        | life   | reased |
| ectron |        |        |        | Arr    |        | time   | at     |
| > mo   |        |        |        | henius |        | 3x107  | Vd=2V  |
| bility |        |        |        | plots  |        | hours  | ope    |
| >      |        |        |        | \[12\] |        | at     | ration |
| transi |        |        |        |        |        | 125C   | with   |
| stors) |        |        |        |        |        | c      | pot    |
| >      |        |        |        |        |        | hannel | ential |
| >      |        |        |        |        |        | temper | realia |
|  AlInA |        |        |        |        |        | ature. | bility |
| s/InGa |        |        |        |        |        | For    | p      |
| As/InP |        |        |        |        |        | Vd=2V, | roblem |
|        |        |        |        |        |        | Ea     | --     |
|        |        |        |        |        |        | dec    | pre    |
|        |        |        |        |        |        | reased | sently |
|        |        |        |        |        |        | to     | an     |
|        |        |        |        |        |        | 0.8eV  | order  |
|        |        |        |        |        |        | \[12\] | of     |
|        |        |        |        |        |        |        | mag    |
|        |        |        |        |        |        |        | nitude |
|        |        |        |        |        |        |        | lower  |
|        |        |        |        |        |        |        | than   |
|        |        |        |        |        |        |        | GaAs   |
|        |        |        |        |        |        |        | c      |
|        |        |        |        |        |        |        | ounter |
|        |        |        |        |        |        |        | parts. |
|        |        |        |        |        |        |        |        |
|        |        |        |        |        |        |        | Hot    |
|        |        |        |        |        |        |        | el     |
|        |        |        |        |        |        |        | ectron |
|        |        |        |        |        |        |        | degra  |
|        |        |        |        |        |        |        | dation |
|        |        |        |        |        |        |        | has    |
|        |        |        |        |        |        |        | also   |
|        |        |        |        |        |        |        | been   |
|        |        |        |        |        |        |        | re     |
|        |        |        |        |        |        |        | ported |
|        |        |        |        |        |        |        | to     |
|        |        |        |        |        |        |        | cause  |
|        |        |        |        |        |        |        | per    |
|        |        |        |        |        |        |        | manent |
|        |        |        |        |        |        |        | ne     |
|        |        |        |        |        |        |        | gative |
|        |        |        |        |        |        |        | thr    |
|        |        |        |        |        |        |        | eshold |
|        |        |        |        |        |        |        | v      |
|        |        |        |        |        |        |        | oltage |
|        |        |        |        |        |        |        | shifts |
|        |        |        |        |        |        |        | \      |
|        |        |        |        |        |        |        | [19\]. |
+--------+--------+--------+--------+--------+--------+--------+--------+
| InP    |        |        | 90     | Tran   |        |        | Pol    |
| HBT    |        |        | Sr/90Y | sistor |        |        | yimide |
| (he    |        |        | 100mCi | curves |        |        | passi  |
| teroju |        |        | be     | (Ic at |        |        | vation |
| nction |        |        | ta-rad | v      |        |        | a      |
| b      |        |        | iation | arious |        |        | ppears |
| ipolar |        |        | source | Ib vs  |        |        | to     |
| transi |        |        | upt to | Vce),  |        |        | in     |
| stors) |        |        | 2.     | DC     |        |        | crease |
| InP/   |        |        | 7x1016 | c      |        |        | rad    |
| InGaAs |        |        | e/cm2  | urrent |        |        | iation |
|        |        |        | (620   | gain   |        |        | resi   |
|        |        |        | Mrad   | (      |        |        | stance |
|        |        |        | (InG   | beta), |        |        | co     |
|        |        |        | AAs))- | beta   |        |        | mpared |
|        |        |        | only   | vs     |        |        | to     |
|        |        |        | 9%     | col    |        |        | e      |
|        |        |        | de     | lector |        |        | arlier |
|        |        |        | crease | cu     |        |        | s      |
|        |        |        | in     | rrent, |        |        | tudies |
|        |        |        | col    | and    |        |        | \      |
|        |        |        | lector | diode  |        |        | [13\]. |
|        |        |        | c      | satu   |        |        |        |
|        |        |        | urrent | ration |        |        |        |
|        |        |        | and    | c      |        |        |        |
|        |        |        | 7.5%   | urrent |        |        |        |
|        |        |        | de     |        |        |        |        |
|        |        |        | crease |        |        |        |        |
|        |        |        | in     |        |        |        |        |
|        |        |        | beta   |        |        |        |        |
|        |        |        | \[13\] |        |        |        |        |
+--------+--------+--------+--------+--------+--------+--------+--------+
| > Re   |        | No     | Slight | RTD    |        |        | Slight |
| sonant |        | change | change | I-V    |        |        | change |
| > tun  |        | in I-V | in IV  | cha    |        |        | in IV  |
| neling |        | cha    | cha    | racter |        |        | curve  |
| >      |        | racter | racter | istics |        |        | after  |
| diodes |        | istics | istics |        |        |        | n      |
| >      |        | after  | after  |        |        |        | eutron |
| (RTDs) |        | 1      | 3.5x10 |        |        |        | irrad  |
| > --   |        | Mra    | 11/cm2 |        |        |        | iation |
| >      |        | d(InP) | 55 MeV |        |        |        | rec    |
| InGaAs |        | using  | p      |        |        |        | overed |
| > and  |        | Co^60^ | rotons |        |        |        | comp   |
| > AlAs |        | gamma  | and    |        |        |        | letely |
| > on   |        | source | after  |        |        |        | at     |
| > InP  |        | \[14\] | 5      |        |        |        | room   |
| > subs |        |        | x10    |        |        |        | tempe  |
| trates |        |        | 10/cm2 |        |        |        | rature |
|        |        |        | high   |        |        |        | after  |
|        |        |        | energy |        |        |        | a few  |
|        |        |        | ne     |        |        |        | hours. |
|        |        |        | utrons |        |        |        |        |
|        |        |        | \[14\] |        |        |        |        |
+--------+--------+--------+--------+--------+--------+--------+--------+

**Reliability and radiation "tall tent poles"\* for specific mission
scenarios in the use of advanced interconnects.**

[Definitions, clarifications and acronyms:]{.underline}

LEO = lower earth orbit (350 to 1400 above earth surface); MEO= medium
or middle earth orbit above LEO and below GEO

GEO = geosynchronous earth orbit, at 35,790 km above earth surface.
Satellites at the geostationary orbit are in GEO and describe a circular
orbit.

Jovian: Jupiter and its moons (Io and Europa)

Long life missions and outer planet exploration will most likely require
nuclear propulsion (Now it is ion propulsion), so a radiation
environment has to be considered.

\* In space jargon, a "tall tent pole" refers to either a critical path
item, or the longest lead-time item.

  -------------- -------------- ---------------- ------------------ --------------- ------------------
  **Mission**    **Thermal      **Mechanical**   **Radiation**      **Chemical      **Other**
                 environment                                        environment**   
                 (includes                                                          
                 thermal                                                            
                 cycles)**                                                          

  LEO, ISS,      Shuttle        Mechanical       No significant     No significant  Micro-meteorites
  Shuttle        reentry        stresses during  concern            concern         
                                launch                                              

  Aeronautics    Same as above  Unknown          Yes, during solar  No significant  Plasma environment
                                                 flares             concern         (spacecraft
                                                                                    charging)

  MEO, GEO       No significant Unknown          Electrons and      No significant  
                 concern unless                  protons. Radiation concern         
                 power is lost                   environments limit                 
                 (cold start)                    electronic life                    
                                                 severely, effect                   
                                                 on metallization                   
                                                 is unknown.                        

  Mars surface,  Average        High winds,      2-5 Kilorads,      Benign          
  low            temperature is mechanical       probably not a                     
  temperature    about 218 K    stresses during  concern in                         
                 (-55 C, -67 F) launch.          metallization                      
                 (lower than                     systems.                           
                 commercial                                                         
                 range).                                                            
                 Surface                                                            
                 temperatures                                                       
                 range widely                                                       
                 from as little                                                     
                 as 140 K (-133                                                     
                 C, -207 F) at                                                      
                 the winter                                                         
                 pole to almost                                                     
                 300 K (27 C,                                                       
                 80 F) on the                                                       
                 dayside in                                                         
                 summer.                                                            

  Jovian system, Extreme cold   Unknown          Yes. Radiation     Unknown         
  outer planets  environments                    effects on                         
                                                 electromigration                   
                                                 are unknown                        

  Outside solar  Extreme cold   Unknown          Yes. Radiation     Probably not a  
  system, very   unless                          effects on         concern         
  long life      electronic is                   electromigration                   
  missions       protected                       are unknown                        

  Venus, rocket  Extreme heat:  Unknown          Unknown but        60 to 90 km of  Atmosphere is very
  and aircraft   absolute                        probably OK        Sulfuric acid   massive by
  engine, other  temperature at                                     clouds.         terrestrial
  high           the surface                                                        standards, with
  temperature.   still unknown                                                      surface pressure
                 but is excess                                                      almost 100 bars
                 of 730 K. 225                                                      (carbon dioxide)
                 day and steep                                                      
                 thermal                                                            
                 changes.                                                           
  -------------- -------------- ---------------- ------------------ --------------- ------------------

**Qualification guidelines, problems, and possibilities**

A good description of qualification methodologies for GaAs MMICs can be
found in the JPL GaAs MMIC reliability assurance guideline for space
applications \[21\] where qualification methodologies are discussed, and
the various acceptance tests targeted for space qualification are
described.

A common problem encountered during some space qualifications of RF
devices, where mean times to failure are to be predicted for
one-of-a-kind type RF devices is that there are often too small sample
sizes to adequately predict reliability under use conditions. The
statistical significance of reliability analysis is directly related to
the sample size used in the various stress tests. Small sample sizes
often force the reliability engineer to waive some of the stress tests,
which is not an optimal situation, especially in high reliability space
applications.

Another problem that reliability engineers often encounter is the lack
of failures. Paradoxically, this is a very undesirable situation. It is
essential to know how devices will fail under use conditions. This is
the first key question that leads to understanding reliability, failures
are considered to be an essential part of each reliability study.
Failures are required to identify root causes of reliability problems,
or to evaluate the weakest link of an IC so that improvements can be
made for the best impact on reliability. Failures also provide the
reference point for future comparisons. If subsequent tests are run
before and after a process change, and they both result in zero
failures, there\'s no way to decide if the process change improved or
impaired the reliability. Most importantly: without a failure, obviously
a failure distribution cannot be determined.

Often times, it is necessary to understand failure mechanisms that
affect each element of a circuit, but this is not possible if ICs are
tested as a whole, since only failure through the weakest link will
occur. Some of the other failure mechanisms might be important to
understand, but their onset in ICs is too slow to be observed compared
to the most predominant failure. In order to measure various failure
mechanisms, it is often necessary to break the ICs into elements in
order to study various component parts on an individual basis. By
breaking ICs into these individual parts or test structures, the failure
mechanisms that uniquely effect each element are more easily identified
and studied.

To predict mean times to failure once test structures or devices are
available, activation energies and acceleration factors can be
determined for several type of use and stress conditions. A few examples
are: current stressing, thermal stressing, a combination of current and
thermal stressing; and testing in humid environments to asses effects of
non-hermetic packages. These stress tests need to be done after setting
up "failure criteria", which is the degradation of some critical device
parameter on a % basis (10% to 20% degradation are typical, sometimes it
can be as high as 50%). For Ohmic contacts the definition of failure
could be, for example, an increase of 50% or more in contact resistance.
For Schottky junctions, increase in leakage current is usually observed
upon stressing, and sometimes an increase in the diode ideality factor.
Therefore, "failure" can be defined as an increase in leakage current
one or two orders of magnitude over the unstressed values.

Recommendations for space use of advanced RF devices and for further
studies:

-   A very important issue in microwave devices is the extrapolation of
    DC electrical characteristics in predicting AC performance. This is
    a very complex issue, and not easy to answer. Device physicists find
    that among several "good" devices, which exhibit similar DC
    electrical characteristics (Current vs voltage is primarily used)
    there are always large variations in the AC performance of devices
    that exhibit similar DC performance. Since high frequency testing is
    more difficult, expensive, and requires special set-ups, finding a
    way to correlate good high-frequency characteristics with some
    measurable (DC) parameter would be a major breakthrough in the areas
    of microelectronics reliability and device characterization.

-   For cryogenic applications of GaAs devices operated in RF
    conditions, hot electron effects are a significantly more relevant
    to the real use conditions. GaAs device manufacturers do not
    typically perform these studies as part of device qualification,
    however hot electron effects tests can provide a more accurate
    assessment of reliability in space applications, so they should be
    performed in space qualification of RF devices.

-   Since most of the NASA applications for GaAs Varactors and mixer
    diodes are based on the characteristics of rectifying
    metal/semiconductor contacts, more is learned in studies that
    isolate the simplest device components and avoid design
    complications. The key device components are the Ohmic contacts and
    the Schottky junctions. GaAs THz devices targeted for THz
    applications use the same type of metallization for Ohmic and
    Schottky contacts. Ohmic contacts are made of Au/Ge/Ni/Ag/Au, and
    Schottky contacts are Ti/Pt/Au. There also promising results that
    use Pd/Ge/Au as Ohmic contacts. For Schottky junctions, Al has given
    very high barrier heights in GaAs, and diffusion of Al into GaAs
    does not cause deep levels. Therefore, these two alternate
    metallization schemes have been proposed for comparative reliability
    studies. Fabrication and testing of test structures should be
    carried for Ohmic contacts of GaAs (at least two types of test
    structures, the transmission line method and the Kelvin cross
    structure); and for Schottky or rectifying junctions and contacts on
    GaAs.

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-   Determination of contact resistance at low temperatures in order to
    answer the questions: Are standard Au/Ge/Ni/Ag/Au Ohmic contacts
    optimized for devices operating at low temperature? Is there a
    better or more reliable metallization scheme for Ohmic contacts to
    GaAs?

-   The evaluation of temperature gradients in devices during operation
    is very important, and as mentioned in previous sections can be a
    reliability concern in space use of GaAs RF devices. This evaluation
    can be performed using cathodoluminescence spectroscopy and imaging
    for example. Determination of the effects of thermal gradients on
    device reliability is a logical follow-up. This is important in some
    applications, for example power multipliers operating at cryogenic
    temperatures -- as in the FIRST/PLANCK mission.

-   As noted earlier, there are many reasons why gallium arsenide
    devices exhibit good reliability, but the primary cause is that
    quality and reliability is built into the process. Each GaAs
    manufacturer has a different \"recipe\" for the fabrication of
    devices, and thus each manufacturer has different strengths and
    weaknesses. In part selection, try by all means to procure RF
    devices from manufacturers that share data from their reliability
    studies.

-   Most common failures are the result of metal/semiconductor
    interdiffusion and radiation is known to enhance diffusion. How
    would radiation damage then affect life-testing results? Are there
    any synergistic effects from radiation in long-term use conditions?

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-   Developing the test infrastructure required to perform life-testing
    on site is very important. The challenge here is the need for at
    speed testing at RF frequencies. This allows changing the conditions
    of the test to adjust to special conditions in space applications.
    One of the needs for infrastructure development, which is common to
    many devices and structures, is the implementation of digital data
    acquisition in real time. Development of the required software,
    hardware and instrumentation is needed to perform the tests
    described here. Furthermore, and more importantly, the experience
    acquired and testing facilities developed are also instrumental in
    supporting flight project needs in future testing of RF devices. The
    development of theoretical background, analytical skills and failure
    analysis tools to allow performing these special tests is also
    strongly recommended.

Timetable for readiness

Compound RF devices are already commercially available. The near term
and long term evolution in GaAs devices is likely to result from
incremental improvements on the maximum cut-off frequency. However, the
area of Terahertz frequencies, or sub millimeter wave applications is an
exception to this statement. Because a number of radically different
approaches and different technologies are being explored to obtain THz
frequencies, some of them will be radically different in just a few
years than technologies used today.

References and bibliography

\[1\]. P. W. Marshall, C. J. Dale, T. Weatherford, M. Carts, D.
McMorrow, A. Peczalski, S. Baier, J. Nohava, and J. Skogen, "Heavy Ion
SEU Immunity of a GaAs Complementary HIGFET Circuit Fabricated on a Low
Temperature Grown Buffer Layer", IEEE Trans. Nucl. Sci., vol. 42, pp.
1850-1855 (1995).

\[2\]. F. Gao and P. Ersland, "Accelerated life tests for High-Speed
0.5-mm InGaAs PHEMT Switches," 1999 GaAs Mantech, Report from
Engineering & Technology, AMP M/A-COM Division.

\[3\]. J. P. Noel et al., "High-reliability blue-shifted InGaAsP/InP
lasers," Appl. Phys. Lett. 69, 3516 (1996).

\[4\]. J. Beringer et al., "radiation hardness and lifetime studies of
LED and VCSELs for the optical readout of the ATLAS SCT," Nucl. Instrum.
Meth A vol 435, p 375 (1999).

\[5\]. N. Dharmarasu et al., "High-radiation-resustant InGaP, InGaAsP,
and InGaAs solar cells for multijunction solar cells,' Appl. Phys.
Lett., vol 79, 2399 (2001).

\[6\]. M. Listvan, P. Vold and D. Arch, "Ionizing radiation hardness of
GaAs Technologies,' IEEE Trans. Nucl. Sci. vol. 43, p1664 (1987).

\[7\]. T. Cunningham et al., "Deep cryogenic noise and electrical
characterization of the complementary heterojunction field-effect
transistor (CHFET)," IEEE Trans. Electron Devices vol 41, p 888 (1994).

\[8\]. C. Wilson et al., "High temperature performance and operation of
HFETs," IEEE Trans. Electron Devices vol 43, p 201 (1996).

\[9\]. K. Lebelsmeyer et al., "Characteristics of GaAs complementary
heterojunction FETs and C-HFET-based amplifiers exposed to high proton
fluences," Nucl. Instrum. Meth A vol 394, p 1-6 (1997).

\[10\]. M.Gallegos, R. Leon, D. T. Vu, and S. Johnson, "Accelerated Life
Testing and Temperature Dependence of Device Characteristics of GaAs
CHFET Devices," to be presented at the International Reliability
Workshop (October 21-24, 2002, Lake Tahoe). 

\[11\]. B. Luo at al., "dc and rf performance of proton-irradiated
AlGaN/GaN high electron mobility transistors," Appl. Phys. Lett. 79,
2196 (2001).

\[12\]. M. Dammann et al., "Effect of drain voltage on channel
temperature and reliability of pseudomorphic InP-based HEMTs,"
Microelectronics Reliability 40, 287 (2000).

\[13\]. A. Shatalov et al., "Electron irradiation effects on polyimide
passivated InP/InGaAs single heterojunction bipolar transistors," IEEE
Trans. Nucl. Sci. vol. 46, p. 1708 (1999).

\[14\]. R. Wilkins et al., "Ionization and displacement damage
irradiation studies of quantum devices: resonant tunneling diodes and
two-dimensional electron gas transistors," IEEE Trans. Nucl. Sci. vol.
46, p. 1702 (1999).

\[15\]. D. Streit et al., "High-reliability GaAs-AlGaAs HBTs by MBE woth
Be base doping and InGaAs emitter contacts," IEEE Electron Dev. Lett.,
vol 12, 471 (1991).

\[16\]. T. Henderson and P. Ikalainen, "Reliability of self-aligned,
ledge passivated 7.5 GHz GaAs/AlGaAs HBT power amplifiers under RF power
stress at elevetad temperatures," IEEE GaAs IC Symposium, Technical
Digest, p 151 (1995).

\[17\]. T Takahashi et al., "High reliability InGaP/GaAs HBTs fabricated
by self-aligned process," IEEE Int. Electron Devices Meeting, Technical
Digest, p. 191 (1994).

\[18\]. S. Bahl et al., "Reliability investigation of InGaP/GaAs
heterojunction bipolar tranaistors," IEEE Int. Electron Devices Meeting,
Technical Digest, p. 815 (1995).

\[19\]. M. Nawaz et al., "Hot electron degradation effects in 0.14
micron AlInAs/InGaAs/InP HEMTs," Microelectronics Reliability 39, 1765
(1999).

\[20\]. M. Dammann et al., "Reliability of InAlAs/InGaAs HEMTs grown on
GaAs substrate with metamorphic buffer," Microelectronics Reliability
40, 1709 (2000).

\[21\]. S. Kayali, G. Ponchak, and R. Shaw, "GaAs MMIC Reliability
assurance guideline for space applications", JPL publication 96-25,
December 15, 1996 (pages 137-167)