The Signatone Triaxial Package
The Signatone Low Current System, combined with a suitable parametric instrument such as the HP4156A, allows measurements of current to the femtoamp (1 x 10 - 15 A) range at temperatures between ambient and 300°C for tests which may predict reliability and future performance such as:
- MOS device sub threshold off currents (click on graph at the right)
- Oxide voltage and charge-to-break-down testing
- Hot carrier degradation and impact ionization current
The components of the Triaxial Package are 1) a triaxially driven room temperature chuck or hot chuck, 2) triaxially driven probe tip holders engineered to operate with a 300°C chuck temperature, 3) a suitable electronically shielded dark box, and 4) appropriate cabling. |
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| Click for larger view |
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| The Triaxial Chuck is available in standard and temperature chuck configurations. Chucks are easily retrofited to Signatone 6 and 8 inch Probe Stations. |
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Triaxial Technology
Triaxial measurements use a 3 conductor system with a driven guard between the source-sense (conductor to be measured) and the signal ground to enable measurements of very low currents. The results are: 1) A low noise floor which is a measure of the effective noise protection of the probe holder or chuck, shielded box, and the HP4156A or equivlaent meter, 2) A high equivalent resistance devinde by 1/Re=dI/dV where Re is the equivalent resistance and dI/dV is the change of current with voltage, and 3) A low residual capacitance defined by I=CrdV/dT. Where I is the forcing current, Cr is the residual capacitance and dV/dT is the change of voltage over time. |
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Topside Measurements
The Signatone Triaxial Package exhibits a typical noise floor of 2 fA and an effective resistance greater than 1 x 10^ 15 ohms when probing on top of the wafer at chuck temperatures to 300°C on a Semi-Automatic prober. The low nosie floor is obtained by use of proprietary materials in both the probe holder and the hot chuck plus the use of triaxial technology. The sub-threshold measurements of Ids vs. Vg are typical of the measurements that can be made. (click on graph at the top right of the page). |
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Substrate Current Measurements
Most parameters may be measured through a top-side contact. If the actual curent flowing through the chuck to ground must be measured, the porperties of the chuck become important. The Triaxial Hot Chuck System has a typical effective noise floor of less than 100fA and an effective resistance of approximately 1x10^ 15 ohms @ 200°C. Although this noise floor will affect the measurement of currents that pass through the chuck, the chuck presents a very quiet environment to devices measured through the topside contacts for measurements of 1 or 2 fA.
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Specifications
| Electrical Characteristics* |
Noise Floor |
Effective Resistance ohms |
@ Chuck Temp |
| Probe tip holder & tip |
+/- 2fA |
>1 x 10^15 |
300°C |
| 6" Chuck |
<30 fA |
>1 x 10^15 |
Ambient |
| 8" Chuck |
<30 fA |
>5 x 10^15 |
Ambient |
| 6" Chuck |
<50 fA |
>5 x 10^15 |
200°C |
| 8" Chuck |
<50 fA |
>5 x 10^15 |
200°C |
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Note:
Measurements made on an HP4156A under long integration with a 10 second hold time and a 1 second delay time after temperature stabilization and zeroing the SMU.
Residual Capacitance*
6" & 8" both @ Ambient & 200°C.....................4 pf typical
Note:
Measured on an HP4156A by recording the voltage change versus time while forcing current with the guard enabled.
| Temperature Parameters |
6" chuck |
8" Chuck |
| Ambient to 200°C typical |
10 min. |
16 min. |
| 200°C to Ambient |
4 min. |
4 min. |
| Uniformity at 200°C |
+/-2°C |
+/-3°C |
| Max Operating Temp. |
300°C |
300°C |
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| Physical Parameters |
Diamete |
Thickness or Length |
Cable Length |
| Probe tip holder |
0.187" |
2.5" |
60" |
| Room Temp. Chuck |
6.5"/8.5" |
0.625" |
60" |
| High Temp. Chuck |
6.5"/8.5" |
1.25" |
60" |
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Applications Notes for low current analysis. |
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