Electrowetting on dielectric(EWOD)allows rapid movement of liquid droplets on a smooth surface,with applications ranging from lab-on-chip devices to micro-actuators.The in-plane force on a droplet is a key indicator o...Electrowetting on dielectric(EWOD)allows rapid movement of liquid droplets on a smooth surface,with applications ranging from lab-on-chip devices to micro-actuators.The in-plane force on a droplet is a key indicator of EWOD performance.This force has been extensively modeled but few direct experimental measurements are reported.We study the EWOD force on a droplet using two setups that allow,for the first time,the simultaneous measurement of force and contact angle,while imaging the droplet shape at 6000 frames/s.For several liquids and surfaces,we observe that the force saturates at a voltage of approximately 150 V.Application of voltages of up 2 kV,that is,10 times higher than is typical,does not significantly increase forces beyond the saturation point.However,we observe that the transient dynamics,localized at the front contact line,do not show saturation with voltage.At the higher voltages,the initial front contact line speed continues to increase,the front contact angle temporarily becomes near zero,creating a thin liquid film,and capillary waves form at the liquid–air interface.When the localized EWOD forces at the contact line exceed the capillary forces,projectile droplets form.Increasing surface tension allows for higher droplet forces,which we demonstrate with mercury.展开更多
The ability to control high-voltage actuator arrays relies, to date, on expensive microelectronic processes or on individual wiring of each actuator to a single off-chip high-voltage switch. Here we present an alterna...The ability to control high-voltage actuator arrays relies, to date, on expensive microelectronic processes or on individual wiring of each actuator to a single off-chip high-voltage switch. Here we present an alternative approach that uses on-chip photoconductive switches together with a light projection system to individually address high-voltage actuators. Each actuator is connected to one or more switches that are nominally OFF unless turned ON using direct light illumination. We selected hydrogenated amorphous silicon (a-Si:H) as our photoconductive material, and we provide a complete characterization of its light to dark conductance, breakdown field, and spectral response. The resulting switches are very robust, and we provide full details of their fabrication processes. We demonstrate that the switches can be integrated into different architectures to support both AC and DC-driven actuators and provide engineering guidelines for their functional design. To demonstrate the versatility of our approach, we demonstrate the use of the photoconductive switches in two distinctly different applications—control of µm-sized gate electrodes for patterning flow fields in a microfluidic chamber and control of cm-sized electrostatic actuators for creating mechanical deformations for haptic displays.展开更多
基金supported by the Swiss National Science Foundation(SNSF)under grant No.200020_184661.
文摘Electrowetting on dielectric(EWOD)allows rapid movement of liquid droplets on a smooth surface,with applications ranging from lab-on-chip devices to micro-actuators.The in-plane force on a droplet is a key indicator of EWOD performance.This force has been extensively modeled but few direct experimental measurements are reported.We study the EWOD force on a droplet using two setups that allow,for the first time,the simultaneous measurement of force and contact angle,while imaging the droplet shape at 6000 frames/s.For several liquids and surfaces,we observe that the force saturates at a voltage of approximately 150 V.Application of voltages of up 2 kV,that is,10 times higher than is typical,does not significantly increase forces beyond the saturation point.However,we observe that the transient dynamics,localized at the front contact line,do not show saturation with voltage.At the higher voltages,the initial front contact line speed continues to increase,the front contact angle temporarily becomes near zero,creating a thin liquid film,and capillary waves form at the liquid–air interface.When the localized EWOD forces at the contact line exceed the capillary forces,projectile droplets form.Increasing surface tension allows for higher droplet forces,which we demonstrate with mercury.
基金We thank S.Shmulevich for useful discussion and continuous support,U.Drechsler for continuous help and support on the microfabrication,the Micro and Nano Fabrication and Printing Unit at Technion where zinc oxide deposition was performed,and particularly G.Ankonina for his help in developing the deposition process,H.Wolf for recording the actuator deformations in Supplementary Movie S4 with his photography equipment,V.B.,and G.V.K.acknowledge R.Allenspach,H.Riel,and W.Riess for their continuous support.We gratefully acknowledge funding from the Israel Science Foundation grant no.2263/20 and the Swiss National Science Foundation grant no.200021_200641.
文摘The ability to control high-voltage actuator arrays relies, to date, on expensive microelectronic processes or on individual wiring of each actuator to a single off-chip high-voltage switch. Here we present an alternative approach that uses on-chip photoconductive switches together with a light projection system to individually address high-voltage actuators. Each actuator is connected to one or more switches that are nominally OFF unless turned ON using direct light illumination. We selected hydrogenated amorphous silicon (a-Si:H) as our photoconductive material, and we provide a complete characterization of its light to dark conductance, breakdown field, and spectral response. The resulting switches are very robust, and we provide full details of their fabrication processes. We demonstrate that the switches can be integrated into different architectures to support both AC and DC-driven actuators and provide engineering guidelines for their functional design. To demonstrate the versatility of our approach, we demonstrate the use of the photoconductive switches in two distinctly different applications—control of µm-sized gate electrodes for patterning flow fields in a microfluidic chamber and control of cm-sized electrostatic actuators for creating mechanical deformations for haptic displays.
