Capacitive MEMS actuator technology platform for inkjet

Introduction

MEMS-based technologies are already commonplace in inkjet print heads for many years. The actuation techniques used can be divided into three main categories:

  • Thermal
  • Piezo
  • Capacitive (or electrostatic).

Whilst all three have a long history, only the first two are being used in commercially available heads. In this article:

  • We will explain why the capacitive actuation technique is an excellent alternative to the more mature thermal and piezo actuation techniques;
  • We will demonstrate how the technology has been matured in a completely different application field (medical ultrasound imaging), and show its feasibility for inkjet applications.

Capacitive actuator basics

 
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The basic operating principle of a capacitive actuator is fairly straightforward: a flexible freestanding membrane is displaced by a voltage between one electrode on the membrane and one on the underlying substrate. This displacement can be used to move fluid.

The main advantages of capacitive actuation compared to piezo-based are:

1.     Manufacturing

  • Easier integration with electronics (“CMOS compatible processing”)
  • Better reproducibility
  • Environmentally friendly (no Pb)
  • Lower production cost

2.     Performance

  • Higher output pressure
  • Larger bandwidth
  • Lower power consumption

CMUT for medical applications

The capacitive actuation (and detection) technology has been developed and matured inside Philips first for the application in medical ultrasound products, so-called CMUT (Capacitive Machined Ultrasound Transducer). Next to the potential for replacing the piezo-based transducers in conventional ultrasound probes, the ability to miniaturize the transducer allows it to be used on top of catheters, for in-body ultrasound imaging.

 Detail of a CMUT array. The circular structures are the flexible membranes

Detail of a CMUT array. The circular structures are the flexible membranes

 CMUT mounted on the tip of a catheter, for use in in-body imaging

CMUT mounted on the tip of a catheter, for use in in-body imaging

Using the medical imaging application domain, we have been able to develop CMUT technology into a mature, manufacturable process.

CMUT technology for inkjet

The inherent advantages of the CMUT technology mentioned above are also relevant for inkjet applications. We have therefore conducted a simulation study to assess the ability of our capacitive actuation technology to generate droplets from an aqueous solution. The picture below is a snapshot of this, showing the feasibility.

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If you want to know more about this technology please visit my presentation at the Digital Printing Conference in Barcelona, or visit the website: https://www.innovationservices.philips.com/looking-expertise/mems-micro-devices/mems-applications/capacitive-micromachined-ultrasonic-transducers-cmut/

Erwin Hijzen, Program Manager
MEMS & Micro Devices, Philips Innovation Services