Study Of NEMS Accelerometer Based On Meso-piezoresistive Effect Of Resonant Tunneling Structure

With the development of MBE(molecular beam epitaxy) and semiconductor NEMS(naonelectro mechanical)devices fabricating technology, there have been more advantageous conditions to design and fabricate superlattice quantum well devices which have been realized. When critical dimension of these devices reaches nano-meter scale, many surprising effects (including quantum effect) will emerge due to the dimension reducing. For example, mechanical-electricsal coupling effect which also called meso-piezoresistive effect, and new mechanical properties are more in an NEMS device. In this paper, according to the obvious mechanical-electrical coupling effect of resonant tunneling superlattice membrane, a NEMS acceleration sensor has been designed and fabricated based on the mesoscopic piezoresistive effects of AlAs / InGaAs double-barrier resonant tunneling membrane structure (RTS).In the first part of this paper, the theory on mechanical-electrical coupling characters of superlattice thin film is introduced, and some physical factors related to the mechanical-electrical coupling characters have been disscussed as well as the relationship between them. Then the AlAs/InGaAs double-barrier superlattice film is designed and grown by MBE in (001) orientation of the GaAs substrate, finally the resonant tunneling film structure at the nanometer scale is designed and fabricated. Besides, a measurement and test system is designed to approve the obvious mechanical-electrical coupling effect of this resonant tunneling film structure. As the result shows: under [110] stress, the resonance peakvoltage of the RTS shifts towards to the positive voltages; under [110] stress, the peak shifts toward to the negative voltages. This result has verified the obvious mechanical-electrical coupling characteristics of the RTS, and has provided some theoretical and experimental support for designing the NEMS accelerometer.In the second part, the structure design of the accelerometer is particular introduced, the structural characteristics of RTS and the accelerometer are discussed respectively. Furthermore, the mechanical properties and frequency characteristics of the accelerometer are simulated and calculated by Ansys finite element analysis software, based on the acoustic analysis theory. Finally, the dimensions of GaAs/AlAs/InGaAs RTS and the accelerometer are given in details.In the next part, an appropriate technological process of the accelerometer is established combined with the molecular beam epitaxy (MBE) and the process of micro-electronics as well as the results of the experiment. The double air-bridges technology is used to decrease the resonant tunneling current and parasitized capacitance, and control holes technology is used to fabricate the four-beams structure. Finally, the process integration of RTS and M/NEMS is realized.In the last part of this paper, the accelerometer has been thoroughly tested. Firstly, several kinds of testing programs together with their testing circuits have been designed based on the requirements of the test and the output characteristics of the accelerometer. According to the different testing methods, oscillation frequency test circuit, bridge test circuit and peak-valley test circuit have been separately designed. These circuits provide the necessary hardware conditions for the test of the accelerometer. Then the static and dynamic characteristics of the accelerometer have been tested on probe station and vibrator. The test results show that: the maximum sensitivity of the sensor reaches 560 mV/g, the resonant frequency of the accelerometer is 2.3 kHz. Quantitative analysis of the impact of pressure on the electrical signal, linear of the sensitivity and linear range have been executed, the results proving that the sensitivity of resonant tunneling micro-structure is an order higher than that of the silicon piezoresistor.All findings in this paper will offer theoretical and experimental basis for the development of the high-sensitivity NEMS sensors based on meso-piezoresistive effect, and of other new high-sensitivity NEMS sensors. So, the findings of this paper are very significant.