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A Fabrication and Measurement Method for a Flexible Ferroelectric Element Based on Van Der Waals Heteroepitaxy
Chapters
Summary April 8th, 2018
In this paper, we present a protocol to directly grow an epitaxial yet flexible lead zirconium titanate memory element on muscovite mica.
Transcript
A Fabrication and Measurement Method for Flexible Ferroelectric Element based on van der Waals Heteroepitaxy.Introduction. Fabricating Flexible PZT Thin Films. Cut a one centimeter by one centimeter mica substrate from a mica sheet with scissors.
Fix this one centimeter by one centimeter mica substrate on a desk, using double-sided tape. Use tweezers to peel off the mica, layer by layer, until the desired thickness, measured with a micrometer. Paste this freshly-cleaved mica substrate on a five inch substrate holder, using a thin layer of silver paint, and cure it at 120 centigrade on a hot plate for 10 minutes to affix mica on a substrate firmly.
Put the PLD substrate holder into the PLD chamber. Select the repetition rate and the laser energy. Move the focusing lens to the set position.
Open the shatter and deposit a five millimeter CFO thin film as the buffer layer, by triggering the laser. Deposit a 20 to 18 millimeter SRO on SAFO buffer layer as the bottom electrode for the subsequent electrical performance tests, by triggering the laser. Deposit a 115 millimeter PZT thin film on the top of SRO bottom electrode, by triggering the laser.
Vent the chamber using a tube, and remove the PZT on mica sample when the temperature reaches room temperature. Put the sample on a piece of glass. Put a pre-designed mesh with 200 micrometer diameter on top of the sample.
Fix the mesh well and put mesh sample into the sputtering chamber. Use CD sputtering to deposit platinum top electrodes on the film. Remove the sample after sputtering.
Use a knife or 20%hydrofluoric acid to remove nearly one millimeter by one millimeter PZT section. This is to uncover the bottom SRO electrode and form many small flexible ferroelectric capacitors. Paint a coat of conductive silver on the exposed SRO to increase the electrical conductivity of the bottom SRO electrode.
Ensure that the conductive silver can contact the exposed SRO. Ferroelectric Characterization Bending Test. On the back side of the flexible sample, glue a piece of paper with the same size as the sample, for easy transfer of the sample from one stage to another.
Place the PZT omega on a tester boat of the ferroelectric tester system in a semiconductor device analyzer. Put one measurement probe of the ferroelectric tester system and the semiconductor device analyzer on the platinum top electrode, and then put the other measurement probe on the silver SRO layer to give the polarization electric field hysteresis loops and the capacitor's electric field curves while the sample is unbent. Measure the P hysteresis loops with the two probes at a two kilohertz frequency and at four Watts.
Measure the CE curves with the two probes at a one megahertz frequency and add four Watts. Remove the ambient sample. Secure the flexible PZT or mica thin film on the disable mode using double-sided tape.
Take care to avoid the slipping or the gliding of the mica during the measurements. Mount it on the tester board of the ferroelectric tester system and the semiconductor device analyzer. Put one probe on the platinum top electrode while the other probe touches the bottom SRO electrode through the silver coding similar to the configuration used earlier.
Measure the P-hysteresis loops and the CE curves under various tinsile and compressive bending radium. Measure the P-hysteresis loops with the two probes at a two kilohertz frequency and add four Watts. Measure the CE curves with the two probes at a one megahertz frequency and add four Watts.
Remove the flexible PZT sample when the PE and the CE measurements are completed. Ferroelectric Characterization Thermal Stability. Put the PZT or mica on the tester boat of the ferroelectric tester system and the semiconductor device analyzer.
Put one measurement probe on the platinum top electrode and put the other measurement probe on the sera SrO layer. Open the temperature control system to heat the sample. Conduct the PE and the CE measurements at different temperatures.
Turn off the heater assembly after the measurements are done. Ferroelectric Characterization Bending Cyclability Tests. Mount the flexible PZT or mica into the two grooves of this setup.
Fix one end of the sample where it is bent from the other end with eight AVO model. Use a ruler to measure the PZT or mica lens along with the movement direction of the motor prior to the eight millimeter bending process. Calculate the movement to lens C to bend the sample five millimeter according to the formula where area is the lens of PZT or mica in a bent state.
R is the bending radia and C is the movement lens of the motor. Set number of bending cycles 1, 000 in the computer. Click the start button to initiate the back and forth motor motion.
Remove the sample and the major VPE to check whether the ferroelectric properties are retained. Representative Results. The epitecture of PZT, SRO, CFO mica thin films were deposited and were supposed to laser the position technique, as outlined in step one.
Figure 1 shows the gross gain and Figure 2 shows an actual flexible MVM element best on the PZT. Mechanical stability is a crucial aspect of flexible device application. The microscope ferroelectric performance of the hetero structure against the mechanic flexing was evaluated on the both tensile and the compressive bending.
Figure 7A and 7B show the PE and the CE hysteresis loops of the PZT capacitors and the various compressive and tensile bending radius. Figure 7C shows the constant of saturated polarization. Residual electric polarization could urge the strands.
And the capacitance values within experimental errors and different bending radius. This results just that the PZT thin film capacitors maintain stable electric practice and the mechanical constraints required for the flexible electronic device application which was also tooked by the raman spectroscopy. The well saturated and the symmetric polarization electric field hysteresis loops and the capacitance electric field with the butterfly curves of the hetero structure measured at one megahertz and the temperature bending from 25 to 175 centigrade for a new device are shown in Fig 8A and 8B, respectively.
This ferroelectric capacitor is at the best constant saturation polarization. A remnant of polarization occurs in field and the capacitance in the wider temperature range as shown in Figure 8C. The hetero structure also maintain high retention and endurance at room temperature as well as at 100 centigrade.
This process imply that the PZT or mica hetero structure can have potential applications in high temperature electronic device. A series of cylability tests were carried out to validate the PZT or mica hetero structures for practical applications. Figure 9 shows PE loops before and after 1, 000 bending cycles in both tinsile and the compressive strain states.
The PE loops at a different bending moves are displayed vertically for the sake of convenience. It is not worthy that the hetero structure retains it's ferroelectric behavior even after 1, 000 bending cycles at a bending radius of five millimeters respective of the natural bending strain.Conclusion.
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