As the arrival of comprehensive hold period, the technical application of the dactylogram below screen became the heat of industry follow, because capacitance plan suffers,be restricted, optics and supersonic plan make development main trend.
Among them, ultrasonic plan uses echo intensity to identify dactylogram, have prevent oil waterproof, penetrability is strong wait for an advantage: Ultrasonic plan uses the ultrasonic scanning finger of the specific frequency that dactylogram model group gives out, because ultrasonic arrives at different capable person to pledge be absorbed when the surface, penetrate with catoptric degree differs, can use the skin and air or different skin layer consequently the difference to sound wave impedance, undertake discriminating to the Ji of dactylogram and the position that valley is in. The advantage of supersonic plan depends on his penetrability is stronger, the hypodermic loops and whorls on a finger that can have depth identifies and can discern live body, the security of plan is consequently higher; in addition, ultrasonic plan gets not easily the interference of oily be soiled and water be soiled and strong light, solution lock is more stable and consequently reliable, already made a when dactylogram identifying plan develops important way.
A few days ago, shanghai Sai Liwei electron is in MEMS is supersonic the last a period of time on the technology research and development of with great concentration, gained revolutionary headway. Its are own the supersonic transducer of research and development already checked through set performance, in 10MHz frequency dot changeover efficiency can be amounted to 1.5% , show superior performance, already used next generation in the research and development that supersonic dactylogram identifies chip.
Think of those who establish small place to use to press report to exceed sonic transducer (the cereal backbone information that PMUT) uses nitrogen to change aluminous piezoelectric effect to undertake the changeover between electric energy and mechanical energy will sense finger skin and dermal layer, in order to make accurate judgement.
Nitrogen melts aluminium is the stuff suppressing report with a kind of very expensive stability, have two main character: Go against piezoelectric effect and piezoelectric effect. Going against piezoelectric effect is to point to when in the material that suppress report two end bring to bear on when voltage, interior of the material that suppress report can produce deformation, form variable and voltage become direct ratio, this is the process; piezoelectric effect that changes electric energy into mechanical energy it is to show the material that suppress report is in below the action of force when generation deformation, the data that suppress report is inside center of negative electric charge produces opposite displacement, make press electric data symbol of two upright generation manacles charge instead, charge volume and pressure become direct ratio, this is the course that changes mechanical energy into electric energy.
Have fasten the craft at other SOI much silicon chip, of Sai Liwei press report to exceed odd silicon chip of sonic transducer original creation to engrave corrode structure and craft, main by change can filmy composition impendingly, include bottom electrode, press electric layer, carry electrode and stretch layer on the head. Use those who press electric data to go against piezoelectric effect, want to fluctuate in film of the material that suppress report only the tension that double bottom electrode and top electrode use consolidate to decide frequency, film is met oscillatory, generation sound wave. And conversely, pass when sound wave change can filmy when, film produces deformation, two end can produce the layer that suppress report to losing contrary accessary charge, periphery circuit can pass an electrode and bottom electrode to collect the telegraphic bugle call of generation.
When undertaking dactylogram identifying applies, bring to bear on to supersonic transducer alternating voltage, supersonic transducer produces vibration, vibration is transmitted up, namely ultrasonic is transmitted up, cross different medium layer (screen, glass) the grain that reachs finger or backbone, sound wave encounters the surface of backbone, partial reflex, partial transmission, and because cereal is hollow angry acoustic resistance fights outclass backbone, so sound wave encounters Gu Shi to be total reflection almost. When the energy of different sound wave that comes back from cereal and backbone reflex passes corresponding supersonic transducer surface, corresponding supersonic transducer can generate different electricity signal (amplitude, frequency, phasic wait for) .
Identify technical program photograph to compare with other dactylogram, supersonic technology can realize 3D dactylogram to identify, security is higher. Adopt the method of acoustics focusing, point to sound wave focusing the surface in one’s hand, if encounter the backbone of finger, partial sound wave is reflexed come back, transmission of the others sound wave enters the skin, after sound wave of this one part encounters dermal layer, be reflexed to come back again so sound wave is in; after encountering backbone, can be in skin and dermal layer are reflexed come back the signal; with two different time and the place in cereal, sound wave is reflexed once only, and it is total reflection signal. Supersonic dactylogram identifies plan to collect skin and dermal dactylogram signal namely through this method, get the dactylogram information of 3D thereby.
The PMUT transducer with successful research and development of Sai Liwei place uses AIN data, be based on CMOS craft, structure of original creation MEMS, simple, facilitating craft achieves the structure. At present course of study already was based on Sai Liwei the research and development that this PMUT transducer has supersonic dactylogram identifies below screen, predict to the quantity will be achieved to produce a standard at the beginning of 2019.