YPS Schottky Thermal Field Emission Sources
YPS Schottky Thermal Field Emission Sources
High brightness, direct replacement electron sources
Introduction
The YPS Schottky TFE source consists of a single crystal (100)
tungsten wire with a very sharp tip including a zirconium reservoir
around the tungsten tip wire
The YPS Schottky type thermal field emission sources are an excellent choice to replace used TFE sources in electron beam systems, including FESEM, SFEG-SEM, FETEM, EPMA, Auger and CD-SEM systems. The YPS sources are drop-in replacements for existing FEI and Denka style sources also known as 184 and 174 type suppressors. The YPS Schottky TFE source consists of a single crystal (100) tungsten wire with a very sharp tip including a zirconium reservoir around the tungsten tip wire. The tip is mounted on a hairpin filament which is used to maintain the tip ate a temperature of around 1800K. This assembly is mounted in a cylindrical suppressor electrode with an aperture through which the sharp tip protrudes. Electrons are emitted from the tip due to both thermal excitation and the electrical field at the tip. The YPS Schottky TFE source tip typically has a radius of 0.3µm and protrudes around 250µm to ensure high brightness of the source.
More info in: Frequently Asked Questions (FAQ) about Thermal Field Emission (TFE)sources
YPS Schottky TFE sources
YPS supplies standard designs, refurbishes legacy designs and designs and supplies custom TFE sources. These products are aimed to customers who are comfortable with changing field emission sources and know how to change, load and align the TFE sources in a clean environment. Operating vacuum for Schottky TFE sources is typically better than 1x10-9mbar. This is higher than the operating vacuum for tungsten or Lab6 sources, but less stringent than for cold field emission sources. The YPS Schottky thermal field emission sources exhibit excellent stability over a wide range of acceleration voltages and long operating times. Electron Source Performance Table
The YPS-174 Schottky TFE module is a drop-in
replacement for the most common standard
Schottky thermal field emitter module.
The YPS-174 Schottky TFE module is a drop-in replacement for the most common standard Schottky thermal field emitter module. It is equivalent in dimensions with both Denka and FEI standard Schottky field emission cathodes. The suppressor aperture has a diameter of 400µm. The emitter typically protrudes 250µm from the suppressor electrode. The YPS-174 is compatible with thermal field emission sources used on E-beam systems from AmRay, Hitachi, JEOL, Zeiss, LEO, Philips, PHI and Riber. Dimensions of the YPS-174 TFE module
The YPS-184 Schottky TFE emitter module
is a drop-in replacement alternative for the
FEI Schottky TFE emitter module.
The YPS-184 Schottky TFE emitter module is a drop-in replacement alternative for the FEI Schottky TFE emitter module. The suppressor aperture has a diameter of 500µm and the emitter protrudes 250µm from the suppressor electrode. The YPS-184 is easy to recognize through the flange at the base. The YPS-184 Schottky TFE module is used in FEI/Philips, CamScan and Tescan FE columns. It can also be found on other systems using an electron beam column with TFE source. . Dimensions of the YPS-184 TFE module
The YPS FEI FEG and SFEG Schottky TFE module is
a complete exchange module assembly replacement
for the FEI TFE module.
The YPS FEI FEG and SFEG Schottky TFE module is a complete exchange module assembly replacement for the FEI TFE module used in the FEI XL-30, Sirion, Inspect and Nova NanoSEM systems. The FEG or SFEG emitter module is supplied within the gun assembly and is factory pre-aligned. It is available for the FEI systems units, the FEG TFE module assembly and for the SFEG Sirion module assembly. This is available as a complete gun module exchange only. The complete TFE gun assembly will be shipped under inert nitrogen gas with a protective container mounted on the gun assembly flange. The type of TFE source can be identified through the silver label on the gun assembly flange.
| Instrument | Product # |
YPS TFE Emitter Module |
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AmRay |
YPS-174-A |
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CamScan |
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YPS-184-C * Exchange only |
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FEI/Philips 174 |
YPS-174-F *Exchange only |
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FEI ** |
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YPS-184-F * Exchange only |
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FEI FEG gun assembly |
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FEG gun assembly exchange only |
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FEI SFEG Sirion gun assembly |
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SFEG gun assembly exchange only |
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Hitachi TFE SEM *** |
YPS-174-H |
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Hitachi TFE CD-SEM |
YPS-174-HC |
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ISI / ABT / Topcon |
YPS-174-IT |
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JEOL |
YPS-174-J |
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LEO (Gemini) |
YPS-174-Z |
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PHI |
YPS-174-P |
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Riber |
YPS-174-R |
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Tescan **** |
YPS-174-T |
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Tescan **** |
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YPS-184-T * Exchange only |
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Zeiss (Gemini) |
YPS-174-Z |
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Custom Emitters |
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** The 184 type TFE emitter module can also be found on other electron beam systems. Contact us for replacement.
*** YPS-174 Schottky TFE emitter modules for Hitachi FESEMS, Hitachi CD-SEMs and JEOL FESEMs are only compatible with Hitachi and JEOL FESEMs which use a thermal field emitter. Cold field emitters are not compatible with the YPS-174 or YPS-184 modules.
**** Tescan uses both 174 and/or 184 type TFE emitter modules .
- Emitter radius value in µm
- Emitter performance @ 1800K
- Temperature versus current graph
- Distance of tip protrudes from the suppressor in µm
- SEM image from the TFE emitter tip
Example of YPS Schottky TFE emitter module data sheet
Ordering information for the YPS Schottky TFE Emitter modules with type 174 suppressor for Amray, Philips, Hitachi, ISI/ABT/Topcon, LEO, PHI, Riber, Tescan and Zeiss columns
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| YPS-174 TFE source dimensions | YPS-184 TFE source dimensions |
Electron Source Performance Table
The electron source performance table is provided to give additional information into the performance and requirements for different type of electron emitters. Tungsten cathodes are still used in many SEMs. Improved results can be obtained with LaB6 cathodes. The highest resolution, highest brightness and best low kV performance can be achieved with either Schottky or cold Field Emission Sources.
Emitter Type |
Thermionic |
Thermionic |
Schottky TFE |
Cold FE |
Tip image comparison |
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Cathode Material |
W |
LaB6 |
ZrO/W (100) |
W (310) |
Operating Temp (K) |
2700 |
1800 |
1800 |
300 |
Cathode Radius (nm) |
60,000 |
10,000 |
<1000 |
<100 |
Effective Source Radius (µm) |
25 |
10 |
0.015 |
0.0025 |
Emission Current Density (A/cm2) |
3 |
30 |
5300 |
17,000 |
Total Emission Current (µA) |
200 |
80 |
200 |
5 |
Brightness (A/cm2.sr.kV) |
1x104 |
1x105 |
1x107 |
2x107 |
Maximum Probe Current (nA) |
1000 |
1000 |
10 |
0.2 |
Energy Spread @ Cathode (ev) |
0.59 |
0.4 |
0.31 |
0.26 |
Energy Spread @ Source Exit (eV) |
1.5 – 2.5 |
1.3 – 2.5 |
0.35 – 0.7 |
0.3 – 0.7 |
Beam Noise (%) |
1 |
1 |
1 |
5 – 10 |
Emission Current Drift (%/h) |
0.1 |
0.2 |
<0.5 |
5 |
Operating Vacuum (hPa/mbar) |
<10-5 |
<10-6 |
<10-8 |
<10-10 |
Typical Cathode Life (h) |
100 |
>1000 |
>5000 |
>2000 |
Cathode Regeneration (h) |
None |
None |
None |
6-12 |
Sensitivity to External Influences |
Minimal |
Low |
Low |
High |
Stability |
Standard |
High |
Very high |
Low |
X-ray analysis |
EDS / WDS |
EDS / WDS |
EDS / WDS |
EDS |
Q. Are TFE sources less reliable than thermionic sources (e.g. Tungsten or LaB6)?
A. No – TFE sources can be very reliable, working over many months continuously. All YPS tips are guaranteed for one year of normal operation
Q. What are the advantages of Schottky thermal field emission compared to cold field emitters e.g. W(310) or W(111)?
A. The major advantages are better beam current stability, higher beam currents, less stringent vacuum requirements and the fact that there is no need for periodic emitter flashing to restore the emission curent.
Q. What are the vacuum requirements for operation of a Schottky thermal field emission source?
A. Normally, 10-9mbar or better at the source region.
Q. What brightness can be achieved with Schottky TFE sources compared to thermionic sources?
A. Schottky TFE emitters have a brightness of about 10xE8 Acm-2sr-1 against 10xE5 Acm-2sr-1 for thermionic sources.
Q. Do Schottky emitters need replacing very frequently?
A. Not really. The lifetime of a Schottky emitter is determined by the life of the Zr reservoir in the tip structure. This is normally about 8000 hours.
Q. Are there special steps to be taken in turning on a Schottky source?
A. Check the vacuum level be 10-9mbar at the emitter. Care is needed to avoid thermal shock to the emitter and to avoid electrical breakdown transients as the extraction voltage is applied. Further, the operating temperature should not exceed 1850K; see data sheet for current/temperature graph.
Q. How do I operate the YPS Schottky TFE emitter?
A. In the same way as other TFE sources. The YPS source is supplied with a Schottky emitter data sheet, unique to each emitter.
Q. How stable is the beam current of a Schottky field emitter compared to a cold field emitter?
A. Beam current stability for the thermal Schottky is <0.5%/h compared to 5-30% drift and random jumps for a cold field emitter.
Q. Can any thermionic source be replaced by a Schottky TFE source?
A. Yes, this is the YPS C>More column upgrade. There will be the need for additional differential pumping at the emitter region and a dedicated HT power supply unit for the TFE source. Contact us for details.
Q. Can a cold field emitter be replaced by a YPS Schottky TFE source?
A. Not as a drop-in replacement. Only when the complete electron gun and HT power supply are replaced. Contact us for details.
