Charge pumping test technique using CMOS ring oscillator on leakage issue

Charge pumping technique has been constantly employed in detecting the distribution of interface defects in metal-oxide-semiconductors field-effect transistor. Unfortunately, the rapid rate at which complementary metal-oxide semiconductors devices are scaling down has seen the equivalent oxide thickness of advanced metal-oxide-semiconductors field-effect transistor reduce even further. This in turn remarkably increases the gate leakage involved in the charge pumping current thereby making it challenging to accurately extract the interface trap density in such metal-oxide-semiconductors field-effect transistor having ultrathin dielectrics. Special pulses with high frequency and short transition time are therefore required to precisely extract the interface trap density, which places great demands on the equipment in current charge pumping measurements. Several techniques have been put forward for separating or diminishing the gate leakage current, however, most of these methods have detrimental shortcomings.

University of Chinese Academy of Sciences researchers developed a novel charge pumping test technique, in which suitable voltage pulses would be produced by a complementary metal-oxide-semiconductor ring oscillator as opposed to equipment. The research team hoped that by using the ring oscillator as the generator of the gate pulse, they would be able to increase the frequency of the gate pulse thereby diminishing gate leakage current. Their research work is now published in Microelectronics Journal.

The research team performed simulations where V-model of trapping model was adopted. They then enabled nonlocal tunneling model so as to account for gate leakage current. Later, they applied a five-level/seven-level ring oscillator. The frequency of gate pulse was tuned by altering the load capacitance. Eventually, they evaluated the output pulse generated by the complementary metal-oxide-semiconductor ring oscillator.

The authors observed that from the simulation results, their approach was capable of simplifying the process of suppressing the tunneling current component in that it enabled extraction of interface trap density more precisely by totally eliminating the influence of gate leakage without any handling with the leakage current. Additionally, the researchers noted that the frequency of the voltage pulses generated by ring oscillator could be readily greater than a single gigahertz.

The Yongbo Liu and colleagues study has presented a novel charge pumping test technique in which voltage pulses have been generated by complementary metal oxide semiconductor ring oscillator instead of the equipment. This new technique has been seen to possess the ability to measure interface trap density more precisely due to its high frequency voltage pulse. Therefore, in their work, the dependency of charge pumping measurement on the hardware has been reduced. This directs that the complementary metal-oxide-semiconductor ring oscillator can be fabricated with CMOS logic circuits. In conclusion, the proposed testing techniques is quite promising for future applications.