Charge Pumping Technique to Measure Polarization Switching Charges of FeFETs

Abstract

This study proposes a new method to measure the polarization charge of ferroelectric field-effect transistors (FeFETs) using a pulse generator and source measurement unit (SMU) and exploiting the charge pumping (CP) principle, which is widely followed to measure the interface trap charge density ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D}_{\text{it}}$ </tex-math></inline-formula> ) of MOSFETs. Although the pulse waveforms applied to the gate electrode were equal to that of conventional polarization charge measurement methods, the response current was measured using the SMU similar to that in CP. As the proposed method measured the average dc current on the well or source/drain terminal, it provided a reliable quantification of polarization charges with low noises even at lower applied voltages. This measurement is possible because the ferroelectric (FE) dipole-induced charge is immovable, similar to an interface charge that is not moved by an interface trap until it recombines with a movable opposite carrier. This method conveniently measured the switching charge even for < 50 ns of rising/falling time of the applied pulse. Moreover, as the read current resolution of the SMU is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 5\times10$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−12</sup> A, the switching charge can be measured with a device area <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ &lt; 1 \boldsymbol {\mu }\text{m}$ </tex-math></inline-formula> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Thus, the proposed CP-based method proved to be a highly effective method of polarization charge measurement for three- or four-terminal devices, such as FeFETs, unless the measurement requires the hysteresis curve along with polarization charges.