System and method for measuring negative bias thermal instability with a ring oscillator
View Patent ↗An integrated circuit, in accordance with one embodiment of the present invention, includes a first device under test (DUT) module coupled to a first ring oscillator module and a second DUT module coupled to a second ring oscillator module. The first DUT module is biased such that interface traps are generated during a first mode. The generated interface traps result in a decrease in a first drive current of the first DUT module. The second device under test module is biased to maintain a reference drive current during the first mode. The operating frequency of the first ring oscillator module, during a second mode, is a function of the first drive current. The operating frequency of the second ring oscillator module, during the second mode, is a function of the reference drive current. The integrated circuit may also include a comparator module for generating an output signal as a function of a difference between the operating frequency of the first and second ring oscillator modules.
1. A method of measuring negative bias thermal instability, said method comprising:
generating a first oscillator signal responsive to a first drive current of a first device under test when in a first mode of operation;
generating a second oscillator signal responsive to a reference drive current of a second device under test when in said first mode of operation; and
determining negative bias thermal instability by comparing said first oscillator signal to said second oscillator signal.
2. The method of claim 1 further comprising:
disabling said first oscillator signal when said first device under test is operating in a second mode of operation; and disabling said second oscillator signal when said second device under test is operating in said second mode of operation.
3. The method of claim 1 further comprising:
generating interface traps operable to decrease said first drive current when said first device under test is operating in a second mode.
4. The method of claim 3 , wherein said generating interface traps results in an increase in a threshold voltage and a decrease in drive current of said first device under test.
5. The method of claim 1 further comprising:
substantially maintaining said reference drive current.
6. The method of claim 1 , wherein said determining further comprises:
generating an output signal that is a function of a difference between said operating frequency of said first oscillator signal and said second oscillator signal.
7. The method of claim 1 , wherein said first device under test and said second device under test comprise at least one transistor.
8. A method of measuring negative bias thermal instability, said method comprising:
biasing a first device under test;
biasing a second device under test;
driving a first oscillator with said first device under test;
driving a second oscillator with said second device under test; and
comparing a first output signal from said first oscillator with a second output signal from said second oscillator to determine negative bias thermal instability.
9. The method of claim 8 further comprising:
enabling said first oscillator signal when said first device under test is operating in a first mode of operation; and enabling said second oscillator signal when said second device under test is operating in said first mode of operation.
10. The method of claim 8 further comprising:
disabling said first oscillator signal when said first device under test is operating in a second mode of operation; and disabling said second oscillator signal when said second device under test is operating in said second mode of operation.
11. The method of claim 8 , wherein said biasing said first device under test comprises:
causing generation of interface traps in said first device under test.
12. The method of claim 11 , wherein said causing leads to an increase in a threshold voltage and to a decrease in drive current of said first device under test.
13. The method of claim 8 , wherein said driving said second oscillator with said second device under test comprises:
generating a substantially constant drive current.
14. The method of claim 8 , wherein said comparing comprises:
generating an output signal representing a function of a difference between a frequency of said first output signal and a frequency of said second output signal.
15. The method of claim 8 , wherein said first device under test and said second device under test each comprise at least one transistor.
16. A method of measuring negative bias thermal instability, said method comprising:
driving a first oscillator with a first device under test biased for generation of interface traps;
driving a second oscillator with a second device under test; and
comparing a first output signal from said first oscillator with a second output signal from said second oscillator to determine negative bias thermal instability.
17. The method of claim 16 , wherein said generation of interface traps leads to an increase in a threshold voltage and a decrease in drive current of said first device under test.
18. The method of claim 16 , wherein said driving said second oscillator with said second device under test comprises:
generating a substantially constant drive current.
19. The method of claim 16 , wherein said comparing comprises:
generating an output signal representing a function of a difference between a frequency of said first output signal and a frequency of said second output signal.
20. The method of claim 16 , wherein said first device under test and said second device under test each comprise at least one transistor.