novel piezoresistive e nose sensor array cell
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Novel piezoresistive e-NOSE sensor array cell V.Stavrov a , - PowerPoint PPT Presentation


  1. ����������������������������������������� ���������������������������������������������� Novel piezoresistive e-NOSE sensor array cell V.Stavrov a , P.Vitanov b , E.Tomerov a , E.Goranova b , G.Stavreva a a Nano ToolShop Ltd., Microelectronica Industrial Zone, 2140 Botevgrad, Bulgaria, b Central Laboratory of Solar Energy and New Energy Sources, Bulgarian Academy of Sciences, 72”Tzarigradsko chaussee”, blvd, 1784 Sofia, Bulgaria

  2. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Content • Introduction • Motivation • Mass-measuring method • Features of proposed MEMS cell • Manufacturing technology • Parameters • Measurement results of MEMS cell • Measurement set-up • Measurement of MEMS cell bonded on PCB carrier • Analyses of resonance frequency measurement • Parallel measurement of MEMS cells • Conclusions Novel piezoresistive e-NOSE sensor array cell

  3. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Motivation Future of analytical and manufacturing methods based on micro-mechanical cantilevers, depends critically on the ability to implement parallel operation and fast signal processing. There are two main reasons: - high throughput requirement and - complexity (multidimensionality) of analyzed value. In order to get parallel function, any single device should be simultaneously: - recognizable, - autonomously actuated and - independently accessible for readout. Devices, fulfilling these requirements, are suffering from a substantial increase in complexity of both: layout and manufacturing technology. In present paper, we demonstrate a novel design of a MEMS (Micro-Electro-Mechanical Systems) cell, dedicated to e-NOSE applications, which solves above mentioned problems. Novel piezoresistive e-NOSE sensor array cell

  4. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Mass-measuring method Fig. (1) - Relation between mass and resonance frequency. ( а ) Resonance frequency and effective mass of the cantilever are correlated by equation (a). A If the mass is changed, it causes resonance frequency change. In first order of (b) approximation, the relation between these changes is given by equation (b). So, Fig. 1 if one measures the resonance frequency shift precisely, the mass-change could be calculated, respectively. Fig. (2). Detection of vibration amplitude by piezoresistor. Deflection of cantilever free end causes stress at it’s base and stress changes piezoresistor value, proportionally to the amplitude. Thus detecting the frequency of Fig. 2 maximum resistivity one can define amplitude resonance. Experimentally, it was found that resistivity change is very small, typically < 0.1%. Fig. (3) Detection of small resistivity changes. Fine resistivity changes of one resistor could be measured by adding another three ones and connecting them in a Wheatstone bridge . Depending on the specific application, one or more bridge resistors are placed on cantilever, but rest to four should be added outside. Various designs with four, two or single piezoresistors integrated on the cantilever have been developed and studied, elsewhere. Fig. 3 Novel piezoresistive e-NOSE sensor array cell

  5. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Features of the proposed MEMS cell 1. It consists of four cantilevers of different length . Each of them has a single piezoresistor embedded at it’s base. 2. All four resistors with same topology are connected in a Wheatstone bridge, together , as shown in Fig. (4). Four I/O pins are enough for power supply and output signal measurement. Fig. 4 3. Integrated bimorph thermo actuator . A bimorph thermo actuator is integrated on cantilevers, as it is shown on Fig. 5. In this particular case, it consists of four serial metal meanders with same topology. Thus, two pins are needed to supply the actuator. How the cell works? Having cantilevers with different resonance frequencies, at every particular vibration frequency, no more than one cantilever is in resonance and it’s resistor value differs from the other ones. Thus, the output voltage of the bridge will be zero for all frequencies except, those around resonance frequencies of individual cantilevers. Fig. 5 Our cell with four cantilevers of different length should have a resonance spectrum, similar to the one, shown in Fig. (6). Ones the resonance spectrum is measured, the Fig. 6 individual cantilevers could be recognized/identified by their resonance frequency. Advantages of proposed new MEMS cell Simple design - just 6 I/O pins, with no performance sacrificed. Frequency recognition of the individual cantilevers is provided. Complete functional device – sensor and actuator. Novel piezoresistive e-NOSE sensor array cell

  6. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Manufacturing technology SiO 2 INITIAL OXYDATION BACK-SIDE 1 Si N-type <100> SiO WET ETCH 2 Si 3 N 4 P+ P+ 5 P+ BORON PATTERN/DOPING P+ P+ 2 FRONT-SIDE DRY ETCH P + P+ 6 RESISTOR PATTERN/DOPING 3 P+ P+ Resistor Heater Al DIE P+ Al P + SEPARATION P+ Al 7 AL-METAL P+ P+ 4 DEPO/PATERN Fig.7a Fig.7b The fabrication process (developed in Nano ToolShop), shown in Fig. 7a and Fig.7b, is based on the double side surface/bulk silicon micromachining. The raw Si wafers: DSP, n-type, <100>, TTV<2 µm , 4 – 6 � .cm. Novel piezoresistive e-NOSE sensor array cell

  7. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Parameters Cantilever dimensions: Lengths - set in the range between 309.5µm and 320 µm Difference in lengths chosen 3.5 µm Pitch 126 µm (width 76 µm, space 50 µm) Thickness variation - wafer-to-wafer between 2.5 and 4.5 µm - die-to-die (on a wafer) up to 2 µm - within one cell ± 0.1 µm Alignment (front/back side) ± 5µm Electrical Parameters Piezoresisor resistance 1500 ± 250 � Thermo-actuator resistance 40 ± 4 � Fig. 8. Scanning electron micrograph of cantilever array with four cantilevers of different length Novel piezoresistive e-NOSE sensor array cell

  8. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Measurement set-up The signal of PC controlled functional generator is supplied to thermo-actuator , shown in Fig. 9. Frequency sweep range of 30 to 75 KHz was used. Wheatstone bridge was supplied by 0.5V DC and its output signal was amplified X 500. RMS of amplified output signal vs. actuator’s frequency Fig. 9 was recorded. Schematic set-up for resonant frequency measurements Novel piezoresistive e-NOSE sensor array cell

  9. �� �������������������� ������ ��������� ���� � ���������������� ����������������������������� Measurement of MEMS cell bonded on PCB carrier Fig.10 а Fig.10b Fig. 11. Resonance spectra of a cell X 4 cantilevers, obtained by using 6 pins In order the read-out the signal, the MEMS cell have been is bonded on a chip carrier made of PCB base material. Once spectra before and after sensor exposure are recorded, the frequency shift of each individual cantilever is corelated to the Fig. 10. Optical micrographs of four- interaction it have been functionalized. cantilever PCB carrier during measuring Novel piezoresistive e-NOSE sensor array cell

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