# How should I approach this diode design problem?

Thread Starter

#### shawn_frost

Joined Dec 20, 2020
2
Hi, is there anyone who can help me/guide me to solve the problem? Even if you could recommend me any teacher, senior, book, or paper, it would be of great help to me. I have come up with a dummy solution, but I am pretty sure it's not that accurate (I can show you my answer). I really appreciate guidance in any form. Thanks for taking the time to read this post!

Suppose there is a piezoelectric crystal 4um * 4 um, thickness 500 nm, with dielectric constant of 10. There are metal electrodes at the top and bottom of the crystal. Suppose ultrasonic waves are applied at a frequency of 1 GHz and ac voltage with peak of 0.3 V is generated across the electrodes. Now suppose a diode and capacitor is connected to the electrodes to create a halfwave rectifier and voltage smoothing circuit.

i> Design (materials, structure, doping etc) the diode and capacitor to obtain best rectification/smoothing, lowering peak-to-peak ripples with the constraints that the area of diode and capacitor should be less than 4um by 4um and thickness less than 500nm.
ii> Design the layout of the circuit (how fabricated structure will look) with the on-chip piezoelectric
iii>Extract the equivalent capacitance across the metal electrodes of the piezoelectric crystal considering all parasitic capacitances. Show all parasitic capacitances in the diagram.

#### LowQCab

Joined Nov 6, 2012
2,032
First, the lowest Forward Voltage Drop I've seen for any Diode is around 0.42 Volts.
There are Active Circuits that get very close to zero with an Op-Amp,
but what's going to power the Op-Amp ???

The Piezo Crystal Structure has Capacitance, the Diode has Capacitance too.
And don't forget ..... the wiring has Inductance, as well as Capacitance.

I think you should actually purchase a Piezo-Electric-Tweeter,
(High Frequency Speaker),
from "Parts Express" you can get one for less than $10.oo US, and then play around with it, take it apart, test it, etc. There are also many articles on tweaking them, different wiring schemes, different uses, etc. . . Thread Starter #### shawn_frost Joined Dec 20, 2020 2 First, the lowest Forward Voltage Drop I've seen for any Diode is around 0.42 Volts. There are Active Circuits that get very close to zero with an Op-Amp, but what's going to power the Op-Amp ??? The Piezo Crystal Structure has Capacitance, the Diode has Capacitance too. And don't forget ..... the wiring has Inductance, as well as Capacitance. I think you should actually purchase a Piezo-Electric-Tweeter, (High Frequency Speaker), from "Parts Express" you can get one for less than$10.oo US,
and then play around with it, take it apart, test it, etc.
There are also many articles on tweaking them, different wiring schemes, different uses, etc.
.
.
Thankyou very much!

#### LesJones

Joined Jan 8, 2017
3,704
I have never heard of any ultrasonic system working at a frequency any where as high as 1 Ghz. I don't think you will find an op amp that will work at that frequency. I think even finding a diode that will work at that frequency will be a problem. The nearest I have seen are microwave germanium diodes but even they have a 0.3 volt forward voltage drop. It may help if you describe the problem you are trying to solve and what you are using to generate ultrasonic waves at 1 Ghz.

Les.

#### crutschow

Joined Mar 14, 2008
29,753
The only rectifying device I know of that can work at that voltage and frequency is a back diode (tunnel diode used in reverse).
They are sometimes used as detectors in sensitive microwave receivers.
Typical characteristic curve shown below:
As you can see, the conduction region goes through 0V without the offset of standard diodes.
For proper operation the forward voltage must not exceed Vpe.