CN107389459A - A kind of thin film mechanical performance real-time test device - Google Patents

Abstract

The invention provides a real-time test device for the mechanical properties of thin films, which belongs to the technical fields of photometric mechanics and material mechanical properties testing. The test device mainly includes a laser deflection measurement part, a pressure loading part, and a film clamping structure. During the test, the stepper motor pushes the cylinder to achieve pressure loading, and the membrane deforms. At the same time, the deflection of the membrane is measured using the principle of Michelson laser interferometry. Pressure and deflection are detected by pressure sensors and silicon photocells, respectively. Programmable FPGA is used to realize stepper motor control, data acquisition and host computer communication, and the host computer realizes data display and processing. The invention combines the optical measurement technology and the principle of the tympanic membrane method to test the mechanical properties of the film, and is suitable for elastic-plastic films with a certain degree of light reflection on the surface.

Description

A real-time test device for mechanical properties of thin films

technical field

The invention combines the optical measurement technology and the principle of the tympanic membrane method to provide a real-time test device for the mechanical properties of thin films, which belongs to the technical fields of optical measurement mechanics and material mechanical properties testing.

Background technique

Thin film is a semiconductor material with excellent mechanical, optical, thermal and electrical properties, which creates conditions for the integration and miniaturization of micro-nano electromechanical system devices. Often used as light-emitting diodes, field effect transistors, protective layers, solar cells and other occasions. Linear one-dimensional and planar two-dimensional suspended thin-film structures are important components of micro-nano electromechanical systems. Testing and improving the mechanical properties of thin-film materials such as elastic modulus and residual stress is the key to improving the stability and reliability of thin-film devices.

The test methods for the mechanical properties of films mainly include tensile method, nano-indentation method, tympanic membrane method, etc. The disadvantage of the stretching method is that it is difficult to overcome the influence of the clamping end, and the film is easily damaged during installation; the nano-indentation method is difficult to overcome the substrate The impact on the mechanical properties of the film is difficult to obtain accurate test results; the tympanic membrane method has a simple principle and high measurement accuracy, which overcomes the shortcomings of the above two methods, and can simultaneously measure multiple parameters, including the elastic modulus and residual stress of the film Wait.

Chinese patent CN106198206A proposes to use the digital speckle correlation method to measure the mechanical properties of the film. During the test, the speckle image needs to be image-processed, the operation is complicated and delayed, and the corresponding relationship between the obtained deflection value and the pressure value is not good; the deflection value is determined by The in-plane displacement is converted from the projection angle, and it is difficult to accurately control the angle value during the test; in order to obtain a better speckle pattern, it is necessary to spray paint on the surface of the film. The thickness of the film is at the micron level or even smaller, and the coating may Performance, the problems mentioned above, the accuracy of the test results of this device is difficult to guarantee.

Negger et al. proposed a micro-scale tympanic membrane test plan in the Journal of Experimental Mechanics in 2014, using a confocal optical microscope combined with a digital image correlation method to measure the three-dimensional deformation of the film. The disadvantage is that the film is prepared by micro-processing technology. The process is complicated. In 2014, Berdova et al. proposed a rod-type tympanic membrane test method to measure the mechanical properties of nano-alumina films in the journal Acta Materialia. This method has the disadvantages of complicated film preparation process and small application range.

Contents of the invention

The purpose of the invention is to provide a real-time testing device for the mechanical properties of thin films.

The technical scheme adopted for realizing the object of the present invention is:

The advantages of the present invention are:

Aiming at the current situation of the testing device for the mechanical properties of the thin film, we propose a real-time testing device for the mechanical properties of the thin film by using the light measurement technology and the principle of the tympanic membrane method. The device is suitable for elastic-plastic films with a certain degree of reflection on the surface. The pressure loading part of the test device is easy to control and has good sealing performance, the deflection measuring part has high measurement accuracy, and the data collection and processing are accurate and real-time. There is no need to treat the surface of the film during the test, and the test results are more accurate; the stepping motor and the cylinder are used for pressure loading, and the pressurization process is stable, easy to control and has good sealing performance; many places in the test device are equipped with multi-axis manual fine-tuning devices, which is convenient Quickly make adjustments before the test; the test device uses the principle of Michelson laser interferometry to measure the deflection, the measurement accuracy is relatively high, and can measure the deflection at the nanometer level; the acrylic glass cube with three interfaces is used as the pressure chamber, which can be pressurized smoothly and can Accurate and real-time detection of pressure values; the use of flanges, test pieces, and rubber gaskets to clamp the film has good sealing performance and has little impact on the accuracy of test results; the use of silicon photocell series resistors to extract interference fringe information is accurate And the real-time performance is good; the programmable logic controller (FPGA) is used to simultaneously collect the voltage value reflecting the pressure and the voltage signal of the silicon photocell in real time, the degree of correspondence between the pressure and the deflection value is high, and the test result is more accurate. The programmable logic controller (FPGA) controls the stepper motor driver and communicates with the host computer. The test device is easy to operate, and the collected experimental data can be calculated without complex processing.

Description of drawings

Figure 1 is a schematic diagram of the overall solution of the present invention.

Fig. 2 is a schematic diagram of the pressure chamber and the film clamping structure.

Figure 3 is a schematic diagram of the principle of the tympanic membrane method.

Figure 4 is a schematic diagram of the connection of silicon photovoltaic cells.

detailed description

Below in conjunction with accompanying drawing 1-4 further illustrate concrete structure and the embodiment of the present invention:

A real-time test device for mechanical properties of thin films, including a pressure loading part, a laser deflection measurement part, and a thin film clamping structure;

The pressure loading part includes a stepping motor 1, a sliding table 3, a cylinder 2, a pressurized air pipe 4, and a pressure chamber 7;

The stepper motor 1 is connected with the stepper motor driver 5;

The ball screw at the output end of the stepping motor 1 is fixed on the support, and the sliding table 3 is penetrated on the ball screw, the sliding table 3 is fixedly connected with the piston rod of the cylinder 2, the cylinder 2 is fixed on the support, and the output end of the cylinder 2 passes through the The pressurized air pipe 4 is connected with the pressure chamber 7;

The pressure chamber 7 is made of acrylic crystal cube, and the first interface 22, the second interface 23 and the third interface 24 are processed inside, the first interface 22 is connected with the film clamping structure 9, and the second interface 23 is connected with the pressurized air pipe 4 , the pressure sensor 6 is connected to the third interface 24, wherein the pressure sensor 6 and the film clamping structure 9 are arranged symmetrically.

The laser deflection measurement part includes a laser 10, a beam expander 11, a dichroic prism 12, a reference plane mirror 16, an imaging light screen 15, and a silicon photocell 14;

The first side of the dichroic prism 12 is arranged corresponding to the film clamping structure 9, and the other second side of the dichroic prism 12 is arranged with a silicon photocell 14 and an imaging light screen 15;

A reference plane mirror 16 is arranged outside the third side of the dichroic prism 12;

A beam expander 11 and a laser 10 are arranged outside the fourth side of the beam splitting prism 12; the laser 10 projects a beam to the beam splitting prism 12 through the beam expander 11, and the beam splitting prism 12 separates two beams, and one beam is projected onto the film clamping structure 9 On the film 26; one path of light beam is projected on the reference plane mirror 16; the light beam reflected by the film 26 and the reference plane mirror 16 is projected on the silicon photocell 14 and the imaging light screen 15 through the dichroic prism to form equi-tilt interference fringes.

Film clamping structure 9 comprises flange 20, test piece table 21, screw 25, rubber washer 27;

The flange 20 is connected to the test piece table 21 through screws 25; a circular groove is arranged in the corresponding surface of the flange plate 20 and the test piece table; the film 26 is clamped by two rubber washers 27, and then placed in the circular groove. fixed in the groove.

The reference plane mirror 16 is installed on the three-degree-of-freedom bracket 17, which can realize the adjustment of front and back, pitch and rotation.

The pressure chamber 7 is placed on the XYZR four-axis manual fine-tuning platform to realize the adjustment of the XYZR four degrees of freedom on the surface of the film 26.

The silicon photocell 14 is installed on the height-adjustable pole 13, and the XZ axis is adjusted according to the position of the center of the interference fringe on the imaging light screen 15; the silicon photocell is used to detect the brightness of the center of the interference fringe.

The silicon photocell 14 is connected in series with the resistor 28, and the intensity of light can be detected by detecting the voltage value at both ends of the resistor.

Also be provided with programmable logic device (FPGA) 19, use programmable logic device (FPGA) 19 to gather the voltage signal of pressure sensor 6 and silicon photovoltaic cell 14; Programmable logic device (FPGA) 19 output control signals to stepper motor driver 5; The device (FPGA) 19 is also connected with the host computer 18 in communication.

Example

Connect the sample stage to the corresponding connection hole on the pressure chamber, and place two rubber gaskets in the circular grooves on the test piece stage and the flange respectively. The depth of the groove is smaller than the thickness of the rubber gasket, so the If there are still protrusions, place the film to be tested between the test piece table and the flange, so that the raised parts of the two rubber gaskets will press the film tightly, and tighten the eight hexagon socket screws evenly distributed on the flange.

Connect one end of the motor driver to the stepper motor, and the other end to the FPGA board, connect the pressure sensor power line to the 24V power supply, and connect the signal line to the FPGA board. The silicon photocell is connected in series with the resistor, and the leads for measuring the voltage across the resistor are connected to the FPGA board.

Turn on the laser, adjust the support of the reference plane mirror and the XYZR four-axis manual fine-tuning platform, so that equi-clinic interference fringes with better roundness appear on the imaging light screen, and at the same time, the laser beam hits the center of the film. Adjust the silicon photocell to the center of the interference fringes. When the deflection of the film changes, the center of the isocline interference fringes will alternately change from bright to dark. Every time the alternation occurs, the value of the deflection change is half the wavelength of the laser, which is 316nm. The output current of the silicon photovoltaic cell has a linear relationship with the light intensity. As the center of the isoclinic interference fringes changes, the output current of the silicon photovoltaic cell changes, and the partial voltage of the series resistor changes accordingly.

Connect the FPGA board to the PC through the serial port, turn on the host computer, click the start button on the host computer, the stepper motor starts to rotate, the pressure starts to load, the membrane deforms, and the center of the isocline interference fringes alternates between bright and dark. The voltage signals of silicon photocells and pressure sensors are collected by FPGA and transmitted to the host computer. The real-time performance is good, and the correspondence between the deflection value and the pressure value is good. The host computer displays and stores the data waveform in real time. Click the stop button on the host computer measurement and control system, the stepper motor stops rotating, and the test is completed.

According to the theoretical model shown in Figure 3, the gradually increasing pressure value and the deflection of the film under the corresponding pressure are obtained from the test, and the mechanical parameters such as the elastic modulus of the film are calculated by using the existing formula.

work process

During the test, the upper computer 18 sends a "start" command, which is transmitted to the programmable device (FPGA) 19 through the serial port, and the programmable device (FPGA) 19 controls the stepping motor 1 to start rotating, and then the sliding table 3 drives the piston rod of the cylinder 2 to move forward. Linear movement, the compressed gas in the cylinder 2 flows to the pressure chamber 7 through the pressurized air pipe 4, and then the pressure in the pressure chamber 7 begins to gradually increase, and the film 26 at the first interface 22 in the pressure chamber 7 is gradually bulged, The pressure sensor 6 at the third interface 24 detects the pressure value in real time.

The beam expanded by the beam expander 11 emitted by the laser 10 is split into two beams through the beam splitter 12, one beam is projected on the film 26 on the film clamping structure 9, and one beam is projected on the reference plane mirror 16; The light beam reflected by the thin film 26 and the reference plane mirror 16 is projected on the silicon photocell 14 and the imaging screen 15 through the dichroic prism to form equi-tilt interference fringes. When the film 26 is gradually inflated by the pressure in the pressure chamber 7, the isoclinic interference fringes will undergo a "swallow" movement, that is, the center of the isoclinic interference fringes will alternately change from bright to dark. The silicon photocell 14 located at the center of the stripe detects the change of light and dark, the current is the largest when it is bright, and the current is the smallest when it is dark.

The pressure value detected by the pressure sensor 6 is reflected by the size of the voltage value, and the alternating light and dark changes of the interference fringes are reflected by the voltage division of the resistor connected in series with the silicon photocell 14. The programmable logic controller (FPGA) 19 collects two voltages simultaneously, and passes The serial port is passed to the upper computer 18. Because the stepper motor 1 is controlled and the voltage is collected through the programmable logic controller (FPGA) 19, so the above-mentioned process is carried out simultaneously.

According to the theoretical model shown in Figure 3, the gradually increasing pressure value and the deflection of the film under the corresponding pressure are obtained from the test, and the mechanical parameters such as the elastic modulus of the film are calculated by using the existing formula.

Claims (8)

1. A kind of 1. thin film mechanical performance real-time test device, it is characterised in that：Including pressure-loaded part, laser deflection metrology portion Divide, film clamp structure；

   Pressure-loaded part includes stepper motor, slide unit, cylinder, pressurization tracheae, pressure chamber；

   Stepper motor is connected with stepper motor driver；

   The ball-screw of stepper motor output end is fixed on bearing, and slide unit is applied on ball-screw, and slide unit is lived with cylinder Stopper rod is fixedly connected, and cylinder is fixed on bearing, and cylinder output end is connected by the tracheae that pressurizes with pressure chamber；

   Pressure chamber is made up of acrylic crystal square, and inside is machined with first interface, second interface and the 3rd interface, first interface Film clamp structure is connected with, second interface is connected with pressurization tracheae, and the 3rd interface is connected with pressure sensor, and wherein pressure passes Sensor and film clamp symmetrical configuration arrangement.
2. 2. thin film mechanical performance real-time test device according to claim 1, it is characterised in that：Laser deflection metrology part Including laser, beam expanding lens, Amici prism, reference planes mirror, imaging optical screen, silicon photocell；

   Amici prism first side arrangement corresponding with film clamp structure, the another second side of Amici prism are disposed with silicon photocell outside With imaging optical screen；

   Amici prism the 3rd is disposed with reference planes mirror outside side；

   Beam expanding lens and laser are arranged outside the side of Amici prism the 4th；Laser by beam expanding lens to Amici prism projecting beam, Amici prism separates two-way light beam, and light beam is projected on the film in film clamp structure all the way；Light beam is incident upon reference all the way On level crossing；Simultaneously shape is incident upon on silicon photocell and imaging optical screen through Amici prism through the light beam that film and reference planes mirror reflect Into equal inclination fringe.
3. 3. thin film mechanical performance real-time test device according to claim 1, it is characterised in that：

   Film clamp structure includes ring flange, specimen stage, screw, rubber washer；

   Ring flange is connected by screw with specimen stage；Circular groove is provided with ring flange and specimen stage corresponding surface；With two rubber Film clamp is subsequently placed in circular groove fixed by packing ring.
4. 4. thin film mechanical performance real-time test device according to claim 1, it is characterised in that：Reference planes mirror is arranged on On Three Degree Of Freedom support, it is possible to achieve front and rear, pitching, the adjustment of rotation.
5. 5. thin film mechanical performance real-time test device according to claim 1, it is characterised in that：Pressure chamber is placed on XYZR On four axle manual fine-tuning platforms, the adjustment of tetra- frees degree of film surface XYZR is realized.
6. 6. thin film mechanical performance real-time test device according to claim 1, it is characterised in that：Silicon photocell is arranged on height Spend on adjustable pole, the adjustment of XZ axle both directions is carried out according to the position at interference fringe center on imaging optical screen；Use silicon Photocell carries out the bright dark detection in interference fringe center.
7. 7. described thin film mechanical performance real-time test device is required according to right 1, it is characterised in that：Silicon photocell and resistance string Connection, the strong and weak detection of illumination is realized by the magnitude of voltage at detection resistance both ends.
8. 8. thin film mechanical performance real-time test device according to claim 1, it is characterised in that：It is additionally provided with Programmable, The voltage signal of pressure sensor and silicon photocell is gathered using Programmable；Programmable outputs control signals to stepper motor Driver；Programmable also communicates to connect with host computer.