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Performance of Precision FH

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Symptoms of 'Too Fast' ... the amplifier delay causes the measured coercive ... Pulse and leakage measurements are more sensitive to amplifier stability than ... – PowerPoint PPT presentation

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Title: Performance of Precision FH


1
Performance of Precision FH
  • Joe T. Evans, Jr.
  • Radiant Technologies, Inc.
  • June 19, 2005

2
High Speed Testing of Ferroelectric Capacitors
  • Ferroelectric capacitors are difficult to test at
    high speed because of their non-linear
    polarization response to the stimulus voltage
  • Three difficulties arise
  • Reflections
  • Overshoot during switching
  • Artificial increases in the coercive voltage.

3
Symptoms of Too Fast
  • When the measured signal is too fast for the
    measurement circuitry, a reflection occurs after
    the peak voltage at Vmax.
  • The plot to the left shows reflections on a 100pF
    linear capacitor.
  • The test period was 3.2µs and the reflection
    oscillated for 0.5µs.
  • The measurement circuitry of the FH does reflect
    within the capacitor areas specified for the
    system.

4
Symptoms of Too Square
  • When the measured capacitor is very square, the
    current generated by the capacitor increases very
    quickly as it begins to switch. The output
    voltage of the measurement circuitry can
    overshoot its proper level trying to keep up
    with the change.
  • Overshoot decreases with longer test periods.
  • The test frequency at which overshoot begins for
    a particular capacitor area increases as the
    capacitor becomes less square.
  • Overshoot determines the test frequency limit on
    the Precision FH.

6µs test on 50µx 50µ PZT capacitor.
5
Overshoot and Pmax
  • Overshoot does not appear to affect the final
    value of Pmax measured on the sample.
  • To the right is plotted the capacitor from the
    previous page at 6µs compared to the same
    capacitor at 3µs, 10µs, and 50µs.

6
Coercive Voltage and Amplification
  • The effect of the amplifier speed on hysteresis
    can be seen on the pages 16 and 17 showing the
    comparison of 50µ x 50µ and 10µ x 10µ PZT
    capacitors measured on the Precision Premier and
    the Precision FH.
  • The absolute value of the Vc of the capacitor as
    measured on the Precision FH is slightly less
    than that measured on the Precision Premier but
    both testers arrive at the same Pmax at Vmax.
  • The Precision FH integrator has a 50MHz amplifier
    with a 350V/µs slew rate while the integrator of
    the Precision Premier has a 4MHz amplifier with a
    350V/µs slew rate.
  • The trade off is that the Precision Premier is
    very stable for long measurements so it has a
    wider frequency range than the FH. But, the FH
    is much faster!

7
Coercive Voltage and Amplification
  • All amplifiers slow down the signal they amplify.
  • On hysteretic capacitors, the amplifier delay
    causes the measured coercive voltage to move out
    from its true value.
  • The faster the amplifier, the more accurate the
    apparent coercive voltage.
  • But, the faster the amplifier, the less stable it
    is for longer measurements.
  • The design of the Precision FH is focused on high
    speed hysteresis loops with the speed and range
    of PUND and Leakage being secondary.

8
Stability and Speed
  • Pulse and leakage measurements are more sensitive
    to amplifier stability than are hysteresis
    measurements.
  • Hysteresis loops are affected as well but can go
    longer than pulse or leakage measurements while
    achieving the same accuracy.
  • This effect is true on all Precision testers.

9
Description of Samples
  • Capacitor Structure (from bottom to top)
  • 5000Å silicon dioxide on lt100gt silicon
  • 400Å titanium dioxide
  • 1500Å polycrystalline lt111gt and lt200gt platinum
  • 2550Å 20/80 SOG PZT deposited in seven layers
  • 1000Å polycrystalline platinum
  • 400Å titanium dioxide
  • 2500Å silicon dioxide
  • Metal interconnect
  • 200Å chromium
  • 2000Å gold
  • A single wafer has capacitors ranging from 16mm2
    to 25µ2.

10
Recovery
  • As has been reported in the past, a DC bias
    applied to a ferroelectric capacitor can reverse
    some imprint effects.
  • The Radiant capacitors are capable of
    withstanding long periods at 9V across their
    2550Å of thickness.
  • Imprint and process degradation effects may be
    100 reversed using the recovery procedure
    recommended below.
  • The capacitors tested in this experiment were
    recovered prior to testing, making them
    extremely square.
  • Recommended Recovery Procedure
  • 9V 1Hz square wave for 100 seconds at room
    temperature.

11
Capacitor Properties as Tested
  • Capacitors with very square switching
    characteristics are difficult to test at high
    frequency because the sudden increase in current
    flow from the capacitor when it starts to switch
    may overwhelm the current cancellation capacity
    of the amplifiers on the RETURN input of the
    tester.
  • The squareness of a ferroelectric capacitor can
    be determined by executing the Normalized
    Capacitance vs Voltage plot filter on a measured
    hysteresis loop of the sample.
  • The capacitors tested for this evaluation
    exceeded 100µF/cm2 during the switch. Typical
    research capacitors usually exhibit about
    30µF/cm2.

12
Capacitor Properties as Tested
  • Radiant focused on qualifying the Precision FH
    for very square capacitors.
  • Ferroelectric capacitors that generate the same
    total charge (Pmax at Vmax) but are not as square
    will more easily be measured by the Precision FH
    at higher speeds.

13
Description of Evaluation
  • The Precision FH is designed to execute high
    speed hysteresis and PUND measurements on
    ferroelectric capacitors.
  • To minimize the effect of cable loading and
    reflections, the dimensions of the FH were set to
    allow it to be placed directly on the probe
    station next to the probes.
  • To evaluate the Precision FH, Radiant executed
    tests of extremely square PZT capacitors directly
    on wafer on a standard probe station.
  • Capacitors with areas within the performance
    range of the FH were tested for hysteresis from
    1µs to 1ms in period.
  • The Precision FH and the Precision Premier
    overlap in their performance ranges at 1KHz
    hysteresis. The same capacitors were measured at
    1KHz on the Premier for comparison to the FH.

14
The FH on the Probe Station
  • The Precision FH enclosure so it can be attached
    to probe stations with magnets.

15
The FH on the Probe Station
  • The coax cable connections from the probes to the
    FH can be very short.

16
Compare Precision FH to Premier
  • 50µ x 50µ PZT capacitor measured on both the FH
    and the Premier.

17
Compare Precision FH to Premier
  • 10µ x 10µ PZT capacitor measured on both the FH
    and the Premier. Averaging was used to minimize
    noise from the Premier. As well, the Premier has
    about 1.5pF of parasitic capacitance which was
    measured and subtracted from its hysteresis loop.
    The parasitic capacitance on the FH is 33fF and
    did not affect this measurement.

18
2500µ2 Capacitor 10µs to 1ms
  • The 2500µ2 capacitor was tested on the x1
    amplification stage of the Precision FH. It has
    a range for square capacitors (gt80µF/cm2 dynamic
    capacitance) from 10µs to 20ms. Capacitors with
    dynamic capacitance around 80µF/cm2 may run
    faster without overshoot.

19
1000µ2 Capacitor 6µs to 1ms
  • The 1000µ2 capacitor was tested on the x1
    amplification stage of the Precision FH.

20
400µ2 Capacitor 4µs to 1ms
  • The 400µ2 capacitor was tested on the x1
    amplification stage of the Precision FH. Note
    the reduced overshoot at the higher speed. The
    smaller area translates to a lower overall charge
    transfer during the test, reducing the overshoot.

21
100µ2 Capacitor 1µs to 1ms
  • The 100µ2 capacitor was tested on the x20
    amplification stage of the Precision FH. This
    area is the optimal area for measurements to 1µ2.

22
25µ2 Capacitor 1µs to 1ms
  • The 25µ2 capacitor was also tested on the x20
    amplification stage of the Precision FH. The
    25µ2 is small enough that it will go as fast as a
    480ns period without overshoot but with some
    extension of the coercive voltage.

23
Summary of Precision FH Performance
Parameter Minimum Maximum 1. Voltage
Range 10V 2. Maximum Hysteresis
Frequency a) 25µ2 500Hz 2MHz
b) 100µ2 500Hz 1MHz c) 400µ2 50Hz 200KHz
d) 1000µ2 50Hz 200KHz e) 2500µ2 50Hz 100KH
z 3. PUND Pulse Widths a) x1 amplification
level 10µs 2ms b) x20 amplification level
200ns 200µs 4. Leakage Measurement
period a) x1 amplification level 200µs 2ms
b) x20 amplification level 200µs 200µs
5. Leakage Measurement Range 50nA 5µA 6. Area
Range (PZT) 5µx5µ 50µx50µ 7. Acquisition Rate per
Point 10ns 8. Clock Rate 100MHz 9. Output
Current 50mA 9. Rise time to 5V 200ns 10. Small
Signal rise time 20ns
24
Summary of Precision FH Performance
  • Power Self-adjusting from 100V to 220V
  • Number of ADC bits 14
  • Number of DAC bits 14
  • Switch over point from the 100MHz clock to the
    200KHz clock for hysteresis 100µs
  • Switch over point from the 100MHz clock to the
    200KHz clock for PUND 40µs
  • Number of points in hysteresis
  • 500ns 50
  • 1µs 100
  • 100µs 5000
  • 1ms 200
  • 20ms 500
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